Check errors by identity, not by message text, in tests (closes #49)

Tests that asserted a failure by a fragment of its message now use
errors.Is: a refactor returning the wrong error, or wrapping with %v
instead of %w, now fails them. New tests return each exported error of
internal/vault and pkg/bip85 that no test returned, and check wrapped
causes (os.ErrNotExist, ErrMnemonicMismatch through GetSecret,
ErrInvalidPathComponent through DeriveBIP85Entropy). The 999-versions
test moves into package secret to name its unexported error. Checks of
errors no test can name keep their text; they are listed on the issue.

Model: opus-5-5

TODO.md

@@ -18,6 +18,13 @@ https://git.eeqj.de/sneak/secret/milestone/12
 
 # Completed Steps
 
+- 2026-10-04: Tests check which error a failure returns with `errors.Is`,
+  not by matching words of its message
+  (https://git.eeqj.de/sneak/secret/issues/49). Every exported error that
+  can be returned has a test that the function returns it, and errors
+  wrapping a cause are checked through the wrapping. Checks that still match
+  text, because the error has no exported value the test can name, are
+  listed on the issue.
 - 2026-10-04: When a vault cannot be opened through its current unlocker,
   because a file the unlocker needs is missing or damaged, its keychain item
   or Secure Enclave key is gone, or the passphrase is wrong, the error now

internal/cli/create_vault_test.go

@@ -66,22 +66,18 @@ func TestCreateExistingVaultChangesNothing(t *testing.T) {
 
 	tests := []struct {
 		command string
-		want    string
 		run     func(c *cli.Instance) error
 	}{
 		{
 			"init",
-			"failed to create default vault: vault default already exists",
 			func(c *cli.Instance) error { return c.Init(cmd) },
 		},
 		{
 			"vault create default",
-			"vault default already exists",
 			func(c *cli.Instance) error { return c.CreateVault(cmd, "default") },
 		},
 		{
 			"vault create work",
-			"vault work already exists",
 			func(c *cli.Instance) error { return c.CreateVault(cmd, "work") },
 		},
 	}
@@ -92,7 +88,7 @@ func TestCreateExistingVaultChangesNothing(t *testing.T) {
 
 			err := tt.run(newCLI(fs))
 
-			require.EqualError(t, err, tt.want)
+			require.ErrorIs(t, err, vault.ErrVaultExists)
 			require.Equal(t, before, snapshotStateDir(t, fs))
 		})
 	}
@@ -227,9 +223,7 @@ func TestStopDuringCreateLeavesWholeVaultOrNone(t *testing.T) {
 		fs := afero.NewMemMapFs()
 		require.NoError(t, fs.MkdirAll(testStateDir, secret.DirPerms))
 
-		requireStopsLeaveWholeVaultOrNone(t, fs, "default",
-			"failed to create default vault: vault default already exists",
-			mnemonic, passphrase,
+		requireStopsLeaveWholeVaultOrNone(t, fs, "default", mnemonic, passphrase,
 			func(c *cli.Instance) error { return c.Init(cmd) })
 	})
 
@@ -239,8 +233,7 @@ func TestStopDuringCreateLeavesWholeVaultOrNone(t *testing.T) {
 		_, err := vault.CreateVault(fs, testStateDir, "default", mnemonic, nil)
 		require.NoError(t, err)
 
-		requireStopsLeaveWholeVaultOrNone(t, fs, "work", "vault work already exists",
-			mnemonic, passphrase,
+		requireStopsLeaveWholeVaultOrNone(t, fs, "work", mnemonic, passphrase,
 			func(c *cli.Instance) error { return c.CreateVault(cmd, "work") })
 	})
 }
@@ -248,9 +241,10 @@ func TestStopDuringCreateLeavesWholeVaultOrNone(t *testing.T) {
 // requireStopsLeaveWholeVaultOrNone checks, as
 // TestStopDuringCreateLeavesWholeVaultOrNone describes, the stops of the
 // command run, creating the vault name on fs with mnemonic and passphrase.
-// Run again where the vault is there, the command must fail with exists.
+// Run again where the vault is there, the command must fail with
+// vault.ErrVaultExists.
 func requireStopsLeaveWholeVaultOrNone(
-	t *testing.T, fs afero.Fs, name, exists string,
+	t *testing.T, fs afero.Fs, name string,
 	mnemonic, passphrase *memguard.LockedBuffer,
 	run func(c *cli.Instance) error,
 ) {
@@ -312,7 +306,7 @@ func requireStopsLeaveWholeVaultOrNone(
 		c.UnlockPassphrase = passphrase
 
 		if _, there := state[vaultDir+"/"]; there {
-			require.EqualError(t, run(c), exists)
+			require.ErrorIs(t, run(c), vault.ErrVaultExists)
 		} else {
 			require.NoError(t, run(c))
 		}

internal/cli/integration_test.go

@@ -680,10 +680,10 @@ func test06GetSecret(t *testing.T, testMnemonic string, runSecret func(...string
 	require.NoError(t, err, "get secret should succeed")
 	assert.Equal(t, "password123", strings.TrimSpace(output), "should return correct secret value")
 
-	// Test that without mnemonic, we get an error
-	output, err = runSecret("get", "database/password")
-	require.Error(t, err, "get should fail without unlock method")
-	assert.Contains(t, output, "failed to unlock vault", "should indicate unlock failure")
+	// Test that without mnemonic, we get an error: the passphrase unlocker
+	// cannot ask for its passphrase, as the tests have no terminal
+	_, err = runSecret("get", "database/password")
+	require.ErrorIs(t, err, secret.ErrPassphraseNotRead, "get should fail without unlock method")
 }
 
 func test07AddSecretVersion(t *testing.T, tempDir, testMnemonic string, runSecret func(...string) (string, error), runSecretWithEnv func(map[string]string, ...string) (string, error), runSecretWithStdin func(string, map[string]string, ...string) (string, error)) {
@@ -839,12 +839,11 @@ func test09GetSpecificVersion(t *testing.T, tempDir, testMnemonic string, runSec
 	assert.Equal(t, "newpassword456", strings.TrimSpace(output), "should return new secret value without --version")
 
 	// An empty --version is not a version; it does not mean the current one
-	output, err = runSecretWithEnv(map[string]string{
+	_, err = runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "get", "--version", "", "database/password")
 
-	require.Error(t, err, "get with an empty version should fail")
-	assert.Contains(t, output, "version '' not found", "should reject the empty version")
+	require.ErrorIs(t, err, vault.ErrVersionNotFound, "should reject the empty version")
 }
 
 func test10PromoteVersion(t *testing.T, tempDir, testMnemonic string, runSecret func(...string) (string, error), runSecretWithEnv func(map[string]string, ...string) (string, error)) {
@@ -1158,11 +1157,7 @@ func testInvalidSecretNames(t *testing.T, testMnemonic string, runSecretWithStdi
 			shouldFail := slices.Contains(definitelyInvalid, invalidName)
 
 			if shouldFail {
-				require.Error(t, err, "add '%s' should fail", invalidName)
-
-				if err != nil {
-					assert.Contains(t, output, "invalid secret name", "should indicate invalid name for '%s'", invalidName)
-				}
+				require.ErrorIs(t, err, vault.ErrInvalidSecretName, "add '%s' should fail", invalidName)
 			} else {
 				// For the slash cases and .hidden, they might succeed
 				// Just log what happened
@@ -1310,9 +1305,8 @@ func test12cCrossVaultMove(t *testing.T, testMnemonic string, runSecretWithEnv f
 	require.NoError(t, err, "add force/test in work should succeed")
 
 	// Move without force should fail
-	output, err = runSecretWithEnv(env, "move", "work:force/test", "default")
-	require.Error(t, err, "move without force should fail when dest exists")
-	assert.Contains(t, output, "already exists", "should indicate destination exists")
+	_, err = runSecretWithEnv(env, "move", "work:force/test", "default")
+	require.ErrorIs(t, err, vault.ErrSecretExists, "move without force should fail when dest exists")
 
 	// Move with force should succeed
 	output, err = runSecretWithEnv(env, "move", "--force", "work:force/test", "default")
@@ -1427,9 +1421,8 @@ func test14SwitchVault(t *testing.T, tempDir string, runSecret func(...string) (
 	require.NoError(t, err, "vault select default should succeed")
 
 	// Test selecting non-existent vault
-	output, err := runSecret("vault", "select", "nonexistent")
-	require.Error(t, err, "selecting non-existent vault should fail")
-	assert.Contains(t, output, "does not exist", "should indicate vault doesn't exist")
+	_, err = runSecret("vault", "select", "nonexistent")
+	require.ErrorIs(t, err, vault.ErrVaultNotFound, "selecting non-existent vault should fail")
 }
 
 func test15VaultIsolation(t *testing.T, testMnemonic string, runSecret func(...string) (string, error), runSecretWithEnv func(map[string]string, ...string) (string, error), runSecretWithStdin func(string, map[string]string, ...string) (string, error)) {
@@ -1450,11 +1443,10 @@ func test15VaultIsolation(t *testing.T, testMnemonic string, runSecret func(...s
 	require.NoError(t, err, "vault select work should succeed")
 
 	// Try to get the default-only secret (should fail)
-	output, err := runSecretWithEnv(map[string]string{
+	_, err = runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "get", "default-only/secret")
-	require.Error(t, err, "should not be able to get default vault secret from work vault")
-	assert.Contains(t, output, "not found", "should indicate secret not found")
+	require.ErrorIs(t, err, vault.ErrSecretNotFound, "should not be able to get default vault secret from work vault")
 
 	// Add a unique secret to work vault
 	_, err = runSecretWithStdin("work-vault-secret", map[string]string{
@@ -1467,14 +1459,13 @@ func test15VaultIsolation(t *testing.T, testMnemonic string, runSecret func(...s
 	require.NoError(t, err, "vault select default should succeed")
 
 	// Try to get the work-only secret (should fail)
-	output, err = runSecretWithEnv(map[string]string{
+	_, err = runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "get", "work-only/secret")
-	require.Error(t, err, "should not be able to get work vault secret from default vault")
-	assert.Contains(t, output, "not found", "should indicate secret not found")
+	require.ErrorIs(t, err, vault.ErrSecretNotFound, "should not be able to get work vault secret from default vault")
 
 	// Verify we can still get the default-only secret
-	output, err = runSecretWithEnv(map[string]string{
+	output, err := runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "get", "default-only/secret")
 	require.NoError(t, err, "get default-only secret should succeed")
@@ -1586,11 +1577,10 @@ func test17ImportFromFile(t *testing.T, tempDir, testMnemonic string, runSecretW
 	// Just verify the import succeeded
 
 	// Test importing non-existent file
-	output, err = runSecretWithEnv(map[string]string{
+	_, err = runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "import", "imported/nonexistent", "--source", "/nonexistent/file")
-	require.Error(t, err, "importing non-existent file should fail")
-	assert.Contains(t, output, "failed", "should indicate failure")
+	require.ErrorIs(t, err, os.ErrNotExist, "importing non-existent file should fail")
 
 	// Verify filesystem structure
 	defaultVaultDir := filepath.Join(tempDir, "vaults.d", "default")
@@ -1905,11 +1895,10 @@ func test23ErrorHandling(t *testing.T, tempDir, secretPath, testMnemonic string,
 	t.Helper()
 
 	// Get non-existent secret
-	output, err := runSecretWithEnv(map[string]string{
+	_, err := runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "get", "nonexistent/secret")
-	require.Error(t, err, "get non-existent secret should fail")
-	assert.Contains(t, output, "not found", "should indicate secret not found")
+	require.ErrorIs(t, err, vault.ErrSecretNotFound, "get non-existent secret should fail")
 
 	// Add secret without mnemonic or unlocker
 	unsetMnemonic := os.Getenv(secret.EnvMnemonic)
@@ -1939,13 +1928,12 @@ func test23ErrorHandling(t *testing.T, tempDir, secretPath, testMnemonic string,
 	// Invalid secret names (already tested in test 12)
 
 	// Non-existent vault operations
-	output, err = runSecret("vault", "select", "nonexistent")
-	require.Error(t, err, "select non-existent vault should fail")
-	assert.Contains(t, output, "does not exist", "should indicate vault doesn't exist")
+	_, err = runSecret("vault", "select", "nonexistent")
+	require.ErrorIs(t, err, vault.ErrVaultNotFound, "select non-existent vault should fail")
 
 	// Import to non-existent vault with test passphrase
 	testPassphrase := "test-passphrase-123" // Define testPassphrase locally
-	output, err = runSecretWithEnv(map[string]string{
+	output, err := runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic:         testMnemonic,
 		secret.EnvUnlockPassphrase: testPassphrase,
 	}, "vault", "import", "nonexistent")
@@ -1953,11 +1941,10 @@ func test23ErrorHandling(t *testing.T, tempDir, secretPath, testMnemonic string,
 	assert.Contains(t, output, "does not exist", "should indicate vault doesn't exist")
 
 	// Get specific version that doesn't exist
-	output, err = runSecretWithEnv(map[string]string{
+	_, err = runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "get", "--version", "99999999.999", "database/password")
-	require.Error(t, err, "get non-existent version should fail")
-	assert.Contains(t, output, "not found", "should indicate version not found")
+	require.ErrorIs(t, err, vault.ErrVersionNotFound, "get non-existent version should fail")
 
 	// Promote non-existent version
 	output, err = runSecretWithEnv(map[string]string{
@@ -2367,11 +2354,10 @@ func test30BackupRestore(t *testing.T, tempDir, secretPath, testMnemonic string,
 	assert.NotEmpty(t, output, "restored secret should have value")
 
 	// Verify post-backup secret is gone
-	output, err = runSecretWithEnv(map[string]string{
+	_, err = runSecretWithEnv(map[string]string{
 		secret.EnvMnemonic: testMnemonic,
 	}, "get", "post-backup/secret")
-	require.Error(t, err, "post-backup secret should not exist after restore")
-	assert.Contains(t, output, "not found", "should indicate secret not found")
+	require.ErrorIs(t, err, vault.ErrSecretNotFound, "post-backup secret should not exist after restore")
 
 	t.Log("Backup and restore completed successfully")
 }
@@ -2436,8 +2422,7 @@ func test31EnvMnemonicUsesVaultDerivationIndex(t *testing.T, tempDir, secretPath
 		t.Logf("Output: %s", getOutput)
 
 		// This is the expected behavior with the current bug
-		require.Error(t, err, "get should fail due to wrong derivation index")
-		assert.Contains(t, getOutput, "derived public key does not match vault", "should indicate key derivation failure")
+		require.ErrorIs(t, err, vault.ErrMnemonicMismatch, "get should fail due to wrong derivation index")
 
 		// Document what should happen when the bug is fixed
 		t.Log("When the bug is fixed, GetValue should read vault metadata and use derivation index 1")

internal/cli/path_traversal_test.go

@@ -154,11 +154,10 @@ func newFsFromSnapshot(t *testing.T, tree map[string]string) afero.Fs {
 }
 
 // requireRejectedAndUnchanged runs a command on a copy of the state
-// directory recorded in before. It requires an error with exactly the
-// message of want, so that a later check rejecting the argument does not
-// count, and everything under the state directory as it was: the error
-// alone proves nothing, since it could come after the vault had already
-// been deleted.
+// directory recorded in before. It requires the error want, so that a later
+// check rejecting the argument does not count, and everything under the
+// state directory as it was: the error alone proves nothing, since it could
+// come after the vault had already been deleted.
 func requireRejectedAndUnchanged(
 	t *testing.T, before map[string]string, want error,
 	run func(c *cli.Instance) error,
@@ -170,7 +169,7 @@ func requireRejectedAndUnchanged(
 	err := run(cli.NewCLIInstanceWithStateDir(fs, testStateDir))
 
 	require.Equal(t, before, snapshotStateDir(t, fs))
-	require.EqualError(t, err, want.Error())
+	require.ErrorIs(t, err, want)
 }
 
 // TestInvalidSecretNameLeavesVaultsUnchanged is a regression test for
@@ -193,77 +192,76 @@ func TestInvalidSecretNameLeavesVaultsUnchanged(t *testing.T) {
 	cmd := &cobra.Command{}
 
 	tests := []struct {
-		command  string
-		rejected string // the secret name the command must reject
-		run      func(c *cli.Instance) error
+		command string
+		run     func(c *cli.Instance) error
 	}{
-		{"rm --force ..", "..", func(c *cli.Instance) error {
+		{"rm --force ..", func(c *cli.Instance) error {
 			return c.RemoveSecret(cmd, "..", true)
 		}},
-		{"rm --force .", ".", func(c *cli.Instance) error {
+		{"rm --force .", func(c *cli.Instance) error {
 			return c.RemoveSecret(cmd, ".", true)
 		}},
-		{`rm --force ""`, "", func(c *cli.Instance) error {
+		{`rm --force ""`, func(c *cli.Instance) error {
 			return c.RemoveSecret(cmd, "", true)
 		}},
-		{"rm --force ../../etc", "../../etc", func(c *cli.Instance) error {
+		{"rm --force ../../etc", func(c *cli.Instance) error {
 			return c.RemoveSecret(cmd, "../../etc", true)
 		}},
-		{"mv --force .. x", "..", func(c *cli.Instance) error {
+		{"mv --force .. x", func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "..", "x", true)
 		}},
-		{"mv --force x ..", "..", func(c *cli.Instance) error {
+		{"mv --force x ..", func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "x", "..", true)
 		}},
-		{`mv --force x ""`, "", func(c *cli.Instance) error {
+		{`mv --force x ""`, func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "x", "", true)
 		}},
 		// "work" is not the current vault: a move within it must not
 		// select it when a name is rejected.
-		{"mv --force work:.. work:x", "..", func(c *cli.Instance) error {
+		{"mv --force work:.. work:x", func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "work:..", "work:x", true)
 		}},
-		{"mv --force work:x work:..", "..", func(c *cli.Instance) error {
+		{"mv --force work:x work:..", func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "work:x", "work:..", true)
 		}},
-		{"mv --force default:.. work", "..", func(c *cli.Instance) error {
+		{"mv --force default:.. work", func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "default:..", "work", true)
 		}},
-		{"mv --force default:.. work:y", "..", func(c *cli.Instance) error {
+		{"mv --force default:.. work:y", func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "default:..", "work:y", true)
 		}},
-		{"mv --force default:x work:..", "..", func(c *cli.Instance) error {
+		{"mv --force default:x work:..", func(c *cli.Instance) error {
 			return c.MoveSecret(cmd, "default:x", "work:..", true)
 		}},
-		{"import --force ..", "..", func(c *cli.Instance) error {
+		{"import --force ..", func(c *cli.Instance) error {
 			return c.ImportSecret(cmd, "..", missingFile, true)
 		}},
-		{"import --force .", ".", func(c *cli.Instance) error {
+		{"import --force .", func(c *cli.Instance) error {
 			return c.ImportSecret(cmd, ".", missingFile, true)
 		}},
-		{"import --force ../../etc", "../../etc", func(c *cli.Instance) error {
+		{"import --force ../../etc", func(c *cli.Instance) error {
 			return c.ImportSecret(cmd, "../../etc", missingFile, true)
 		}},
-		{"version list ..", "..", func(c *cli.Instance) error {
+		{"version list ..", func(c *cli.Instance) error {
 			return c.ListVersions(cmd, "..")
 		}},
-		{"version promote ..", "..", func(c *cli.Instance) error {
+		{"version promote ..", func(c *cli.Instance) error {
 			return c.PromoteVersion(cmd, "..", testVersion)
 		}},
-		{"version rm --force ..", "..", func(c *cli.Instance) error {
+		{"version rm --force ..", func(c *cli.Instance) error {
 			return c.RemoveVersion(cmd, "..", testVersion, true)
 		}},
-		{"encrypt ..", "..", func(c *cli.Instance) error {
+		{"encrypt ..", func(c *cli.Instance) error {
 			return c.Encrypt("..", "", "")
 		}},
-		{"decrypt ..", "..", func(c *cli.Instance) error {
+		{"decrypt ..", func(c *cli.Instance) error {
 			return c.Decrypt("..", "", "")
 		}},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.command, func(t *testing.T) {
-			requireRejectedAndUnchanged(t, before, vault.ValidateSecretName(tt.rejected), tt.run)
+			requireRejectedAndUnchanged(t, before, vault.ErrInvalidSecretName, tt.run)
 		})
 	}
 }
@@ -299,10 +297,18 @@ func TestInvalidVersionLeavesVaultsUnchanged(t *testing.T) {
 	for _, tt := range commands {
 		for _, version := range []string{"", ".", "..", "../../..", "a/b"} {
 			t.Run(fmt.Sprintf("%s %q", tt.command, version), func(t *testing.T) {
+				fs := newFsFromSnapshot(t, before)
+
+				err := tt.run(cli.NewCLIInstanceWithStateDir(fs, testStateDir), version)
+
+				require.Equal(t, before, snapshotStateDir(t, fs))
+
+				// Compared as text: `version rm` and `version promote` return
+				// internal/cli's own error of this text, which errors.Is does
+				// not match to vault.ErrVersionNotFound.
 				want := fmt.Errorf("version '%s' %w '%s'",
 					version, vault.ErrVersionNotFound, "x")
-				requireRejectedAndUnchanged(t, before, want,
-					func(c *cli.Instance) error { return tt.run(c, version) })
+				require.EqualError(t, err, want.Error())
 			})
 		}
 	}
@@ -355,7 +361,7 @@ func TestInvalidVaultNameLeavesStateUnchanged(t *testing.T) {
 	for _, tt := range commands {
 		for _, name := range []string{"", ".", "..", "a/b"} {
 			t.Run(fmt.Sprintf(tt.command, name), func(t *testing.T) {
-				requireRejectedAndUnchanged(t, before, vault.ValidateVaultName(name),
+				requireRejectedAndUnchanged(t, before, vault.ErrInvalidVaultName,
 					func(c *cli.Instance) error {
 						c.Mnemonic = mnemonic
 						c.UnlockPassphrase = passphrase

internal/cli/secrets_size_test.go

@@ -93,8 +93,8 @@ func newSizeTestVault(t *testing.T) (afero.Fs, *vault.Vault) {
 }
 
 // runAddSecretSizeCase adds a secret of the given size through stdin and
-// verifies the outcome.
-func runAddSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string) {
+// verifies the outcome: wantErr, or the secret stored when wantErr is nil.
+func runAddSecretSizeCase(t *testing.T, size int, wantErr error) {
 	t.Helper()
 	skipIfLockedMemoryTooLow(t, size)
 
@@ -128,9 +128,8 @@ func runAddSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string) {
 	secretName := fmt.Sprintf("test-secret-%d", size)
 	err = cli.AddSecret(secretName, false)
 
-	if wantErr {
-		require.Error(t, err)
-		assert.Contains(t, err.Error(), errMsg)
+	if wantErr != nil {
+		require.ErrorIs(t, err, wantErr)
 
 		return
 	}
@@ -148,8 +147,8 @@ func runAddSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string) {
 }
 
 // runImportSecretSizeCase imports a secret file of the given size and
-// verifies the outcome.
-func runImportSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string) {
+// verifies the outcome: wantErr, or the secret stored when wantErr is nil.
+func runImportSecretSizeCase(t *testing.T, size int, wantErr error) {
 	t.Helper()
 	skipIfLockedMemoryTooLow(t, size)
 
@@ -181,9 +180,8 @@ func runImportSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string
 	secretName := fmt.Sprintf("imported-secret-%d", size)
 	err = cli.ImportSecret(cmd, secretName, testFile, false)
 
-	if wantErr {
-		require.Error(t, err)
-		assert.Contains(t, err.Error(), errMsg)
+	if wantErr != nil {
+		require.ErrorIs(t, err, wantErr)
 
 		return
 	}
@@ -205,57 +203,48 @@ func runImportSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string
 //nolint:paralleltest // together the subtests lock more than the memlock limit
 func TestAddSecretVariousSizes(t *testing.T) {
 	tests := []struct {
-		name        string
-		size        int
-		shouldError bool
-		errorMsg    string
+		name    string
+		size    int
+		wantErr error
 	}{
 		{
-			name:        "1KB secret",
-			size:        1024,
-			shouldError: false,
+			name: "1KB secret",
+			size: 1024,
 		},
 		{
-			name:        "10KB secret",
-			size:        10 * 1024,
-			shouldError: false,
+			name: "10KB secret",
+			size: 10 * 1024,
 		},
 		{
-			name:        "100KB secret",
-			size:        100 * 1024,
-			shouldError: false,
+			name: "100KB secret",
+			size: 100 * 1024,
 		},
 		{
-			name:        "1MB secret",
-			size:        1024 * 1024,
-			shouldError: false,
+			name: "1MB secret",
+			size: 1024 * 1024,
 		},
 		{
-			name:        "10MB secret",
-			size:        10 * 1024 * 1024,
-			shouldError: false,
+			name: "10MB secret",
+			size: 10 * 1024 * 1024,
 		},
 		{
-			name:        "99MB secret",
-			size:        99 * 1024 * 1024,
-			shouldError: false,
+			name: "99MB secret",
+			size: 99 * 1024 * 1024,
 		},
 		{
-			name:        "100MB secret minus 1 byte",
-			size:        100*1024*1024 - 1,
-			shouldError: false,
+			name: "100MB secret minus 1 byte",
+			size: 100*1024*1024 - 1,
 		},
 		{
-			name:        "101MB secret - should fail",
-			size:        101 * 1024 * 1024,
-			shouldError: true,
-			errorMsg:    "secret too large: exceeds 100MB limit",
+			name:    "101MB secret - should fail",
+			size:    101 * 1024 * 1024,
+			wantErr: errSecretTooLarge,
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			runAddSecretSizeCase(t, tt.size, tt.shouldError, tt.errorMsg)
+			runAddSecretSizeCase(t, tt.size, tt.wantErr)
 		})
 	}
 }
@@ -265,57 +254,48 @@ func TestAddSecretVariousSizes(t *testing.T) {
 //nolint:paralleltest // together the subtests lock more than the memlock limit
 func TestImportSecretVariousSizes(t *testing.T) {
 	tests := []struct {
-		name        string
-		size        int
-		shouldError bool
-		errorMsg    string
+		name    string
+		size    int
+		wantErr error
 	}{
 		{
-			name:        "1KB file",
-			size:        1024,
-			shouldError: false,
+			name: "1KB file",
+			size: 1024,
 		},
 		{
-			name:        "10KB file",
-			size:        10 * 1024,
-			shouldError: false,
+			name: "10KB file",
+			size: 10 * 1024,
 		},
 		{
-			name:        "100KB file",
-			size:        100 * 1024,
-			shouldError: false,
+			name: "100KB file",
+			size: 100 * 1024,
 		},
 		{
-			name:        "1MB file",
-			size:        1024 * 1024,
-			shouldError: false,
+			name: "1MB file",
+			size: 1024 * 1024,
 		},
 		{
-			name:        "10MB file",
-			size:        10 * 1024 * 1024,
-			shouldError: false,
+			name: "10MB file",
+			size: 10 * 1024 * 1024,
 		},
 		{
-			name:        "99MB file",
-			size:        99 * 1024 * 1024,
-			shouldError: false,
+			name: "99MB file",
+			size: 99 * 1024 * 1024,
 		},
 		{
-			name:        "100MB file",
-			size:        100 * 1024 * 1024,
-			shouldError: false,
+			name: "100MB file",
+			size: 100 * 1024 * 1024,
 		},
 		{
-			name:        "101MB file - should fail",
-			size:        101 * 1024 * 1024,
-			shouldError: true,
-			errorMsg:    "secret file too large: exceeds 100MB limit",
+			name:    "101MB file - should fail",
+			size:    101 * 1024 * 1024,
+			wantErr: errSecretFileTooLarge,
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			runImportSecretSizeCase(t, tt.size, tt.shouldError, tt.errorMsg)
+			runImportSecretSizeCase(t, tt.size, tt.wantErr)
 		})
 	}
 }

internal/cli/version_test.go

@@ -171,8 +171,7 @@ func TestListVersionsNonExistentSecret(t *testing.T) {
 
 	// Try to list versions of non-existent secret
 	err := cli.ListVersions(cmd, "nonexistent/secret")
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "not found")
+	require.ErrorIs(t, err, errSecretNotFound)
 }
 
 func TestPromoteVersionCommand(t *testing.T) {
@@ -266,8 +265,7 @@ func TestPromoteNonExistentVersion(t *testing.T) {
 
 	// Try to promote non-existent version
 	err = cli.PromoteVersion(cmd, "test/secret", "20991231.999")
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "not found")
+	require.ErrorIs(t, err, errVersionNotFound)
 }
 
 func TestGetSecretWithVersion(t *testing.T) {

internal/secret/keychainunlocker_test.go

@@ -72,9 +72,12 @@ func TestKeychainInvalidItemName(t *testing.T) {
 	testData := memguard.NewBufferFromBytes([]byte("test"))
 	defer testData.Destroy()
 
+	// Test an empty item name
+	err := storeInKeychain("", testData)
+	require.ErrorIs(t, err, errKeychainItemNameEmpty)
+
 	// Test invalid item names
 	invalidNames := []string{
-		"",                  // Empty name
 		"test space",        // Contains space
 		"test/slash",        // Contains slash
 		"test\\backslash",   // Contains backslash
@@ -96,9 +99,8 @@ func TestKeychainInvalidItemName(t *testing.T) {
 
 	for _, name := range invalidNames {
 		err := storeInKeychain(name, testData)
-		assert.Error(t, err, "Expected error for invalid name: %s", name)
-		assert.Contains(t, err.Error(), "invalid keychain item name",
-			"Error should mention invalid name for: %s", name)
+		require.ErrorIs(t, err, errInvalidKeychainItemName,
+			"Expected error for invalid name: %s", name)
 	}
 
 	// Test valid names (should not error on validation)

internal/secret/seunlocker_test.go

@@ -4,6 +4,7 @@
 package secret
 
 import (
+	"os"
 	"testing"
 	"time"
 
@@ -106,6 +107,5 @@ func TestSecureEnclaveUnlockerGetIdentityMissingFile(t *testing.T) {
 	// GetIdentity should fail because the encrypted longterm key file is missing
 	identity, err := unlocker.GetIdentity()
 	assert.Nil(t, identity)
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "failed to read SE-encrypted long-term key")
+	require.ErrorIs(t, err, os.ErrNotExist)
 }

internal/secret/version_internal_test.go

@@ -0,0 +1,31 @@
+package secret
+
+import (
+	"fmt"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenerateVersionNameMaxSerial(t *testing.T) {
+	t.Parallel()
+
+	fs := afero.NewMemMapFs()
+	secretDir := "/test/secret"
+	versionsDir := filepath.Join(secretDir, "versions")
+
+	// Create 999 versions
+	today := time.Now().Format("20060102")
+	for i := 1; i <= 999; i++ {
+		versionName := fmt.Sprintf("%s.%03d", today, i)
+		err := fs.MkdirAll(filepath.Join(versionsDir, versionName), 0o755)
+		require.NoError(t, err)
+	}
+
+	// Try to create one more - should fail
+	_, err := GenerateVersionName(fs, secretDir)
+	require.ErrorIs(t, err, errMaxVersionsPerDay)
+}

internal/secret/version_test.go

@@ -36,7 +36,6 @@ package secret_test
 
 import (
 	"errors"
-	"fmt"
 	"path/filepath"
 	"testing"
 	"time"
@@ -127,27 +126,6 @@ func TestGenerateVersionName(t *testing.T) {
 	assert.NotEqual(t, version1, version2)
 }
 
-func TestGenerateVersionNameMaxSerial(t *testing.T) {
-	t.Parallel()
-
-	fs := afero.NewMemMapFs()
-	secretDir := testSecretDir
-	versionsDir := filepath.Join(secretDir, "versions")
-
-	// Create 999 versions
-	today := time.Now().Format("20060102")
-	for i := 1; i <= 999; i++ {
-		versionName := fmt.Sprintf("%s.%03d", today, i)
-		err := fs.MkdirAll(filepath.Join(versionsDir, versionName), 0o755)
-		require.NoError(t, err)
-	}
-
-	// Try to create one more - should fail
-	_, err := secret.GenerateVersionName(fs, secretDir)
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "exceeded maximum versions per day")
-}
-
 func TestNewVersion(t *testing.T) {
 	t.Parallel()
 

internal/vault/errors_test.go

@@ -0,0 +1,136 @@
+package vault_test
+
+import (
+	"path/filepath"
+	"testing"
+
+	"git.eeqj.de/sneak/secret/internal/secret"
+	"git.eeqj.de/sneak/secret/internal/vault"
+	"github.com/awnumar/memguard"
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	// otherMnemonic is a valid BIP39 mnemonic other than testMnemonic.
+	otherMnemonic = "legal winner thank year wave sausage worth useful " +
+		"legal winner thank yellow"
+
+	// missingName names no vault, secret or unlocker.
+	missingName = "missing"
+)
+
+// newErrorTestVault creates the vault testVaultName, with the secret
+// testSecretName in it, on a new in-memory filesystem.
+func newErrorTestVault(t *testing.T) *vault.Vault {
+	t.Helper()
+
+	vlt, err := vault.CreateVault(afero.NewMemMapFs(), testStateDir,
+		testVaultName, testMnemonicBuffer(t), nil)
+	require.NoError(t, err)
+
+	value := memguard.NewBufferFromBytes([]byte("value"))
+	t.Cleanup(value.Destroy)
+
+	require.NoError(t, vlt.AddSecret(testSecretName, value, false))
+
+	return vlt
+}
+
+// TestVaultErrors checks that each failure returns its exported error,
+// wrapped or not, so that errors.Is tells it apart from the others.
+func TestVaultErrors(t *testing.T) {
+	t.Parallel()
+
+	vaultDir := filepath.Join(testStateDir, "vaults.d", testVaultName)
+
+	tests := []struct {
+		name string
+		run  func(vlt *vault.Vault) error
+		want error
+	}{
+		{"create an existing vault", func(vlt *vault.Vault) error {
+			_, err := vault.CreateVault(vlt.GetFilesystem(), testStateDir,
+				testVaultName, nil, nil)
+
+			return err
+		}, vault.ErrVaultExists},
+		{"select a missing vault", func(vlt *vault.Vault) error {
+			return vault.SelectVault(vlt.GetFilesystem(), testStateDir, missingName)
+		}, vault.ErrVaultNotFound},
+		{"add a nil value", func(vlt *vault.Vault) error {
+			return vlt.AddSecret(missingName, nil, false)
+		}, vault.ErrNilValueBuffer},
+		{"get a missing secret", func(vlt *vault.Vault) error {
+			_, err := vlt.GetSecret(missingName)
+
+			return err
+		}, vault.ErrSecretNotFound},
+		{"copy onto an existing secret", func(vlt *vault.Vault) error {
+			return vlt.CopySecretAllVersions(vlt, testSecretName, testSecretName, false)
+		}, vault.ErrSecretExists},
+		{"copy a secret without versions", func(vlt *vault.Vault) error {
+			err := vlt.GetFilesystem().MkdirAll(
+				filepath.Join(vaultDir, "secrets.d", missingName), secret.DirPerms)
+			if err != nil {
+				return err
+			}
+
+			return vlt.CopySecretAllVersions(vlt, missingName, "copy", false)
+		}, vault.ErrNoVersions},
+		{"remove a missing unlocker", func(vlt *vault.Vault) error {
+			return vlt.RemoveUnlocker(missingName)
+		}, vault.ErrUnlockerNotFound},
+		{"select a missing unlocker", func(vlt *vault.Vault) error {
+			return vlt.SelectUnlocker(missingName)
+		}, vault.ErrUnlockerNotFound},
+		{"unlocker of an unknown type", func(vlt *vault.Vault) error {
+			fs := vlt.GetFilesystem()
+
+			err := afero.WriteFile(fs,
+				filepath.Join(vaultDir, "unlockers.d", "odd", "unlocker-metadata.json"),
+				[]byte(`{"type":"odd"}`), secret.FilePerms)
+			if err != nil {
+				return err
+			}
+
+			err = afero.WriteFile(fs, filepath.Join(vaultDir, "current-unlocker"),
+				[]byte("odd"), secret.FilePerms)
+			if err != nil {
+				return err
+			}
+
+			_, err = vlt.GetCurrentUnlocker()
+
+			return err
+		}, vault.ErrUnsupportedUnlockerType},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			require.ErrorIs(t, tt.run(newErrorTestVault(t)), tt.want)
+		})
+	}
+}
+
+// TestGetSecretWithWrongMnemonic checks that getting a secret that exists,
+// from a vault the given mnemonic does not open, fails with
+// ErrMnemonicMismatch through GetSecret's wrapping, and not with
+// ErrSecretNotFound.
+func TestGetSecretWithWrongMnemonic(t *testing.T) {
+	t.Parallel()
+
+	created := newErrorTestVault(t)
+
+	mnemonic := memguard.NewBufferFromBytes([]byte(otherMnemonic))
+	t.Cleanup(mnemonic.Destroy)
+
+	vlt := vault.NewVault(created.GetFilesystem(), testStateDir, testVaultName)
+	vlt.SetMnemonic(mnemonic)
+
+	_, err := vlt.GetSecret(testSecretName)
+	require.ErrorIs(t, err, vault.ErrMnemonicMismatch)
+	require.NotErrorIs(t, err, vault.ErrSecretNotFound)
+}

internal/vault/integration_test.go

@@ -2,6 +2,7 @@ package vault_test
 
 import (
 	"bytes"
+	"errors"
 	"os"
 	"path/filepath"
 	"slices"
@@ -341,9 +342,9 @@ func testVaultNameValidation(t *testing.T, fs afero.Fs, tempDir string) {
 
 	for _, name := range invalidNames {
 		_, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t), nil)
-		if err == nil {
-			t.Errorf("Expected error creating vault with invalid name %q, "+
-				"but got none", name)
+		if !errors.Is(err, vault.ErrInvalidVaultName) {
+			t.Errorf("Expected ErrInvalidVaultName creating vault with "+
+				"invalid name %q, got %v", name, err)
 		}
 	}
 }

internal/vault/integration_version_test.go

@@ -320,10 +320,10 @@ func testVersionSerialLimits(
 	err = fs.MkdirAll(filepath.Join(secretDir, versionName), 0o755)
 	require.NoError(t, err)
 
-	// Should fail to create 1000th version
+	// Should fail to create 1000th version. The error is unexported in
+	// package secret, whose own test checks that it is the one returned.
 	_, err = secret.GenerateVersionName(fs, filepath.Dir(secretDir))
 	require.Error(t, err)
-	assert.Contains(t, err.Error(), "exceeded maximum versions per day")
 }
 
 func testVersionErrorCases(t *testing.T, vault *Vault, secretName string) {
@@ -331,20 +331,18 @@ func testVersionErrorCases(t *testing.T, vault *Vault, secretName string) {
 
 	// Try to get non-existent version
 	_, err := vault.GetSecretVersion(secretName, "99991231.999")
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "not found")
+	require.ErrorIs(t, err, ErrVersionNotFound)
 
 	// Try to get version of non-existent secret
 	_, err = vault.GetSecretVersion("nonexistent/secret", "")
-	require.Error(t, err)
+	require.ErrorIs(t, err, ErrSecretNotFound)
 
 	// Try to add secret without force when it exists
 	failBuffer := memguard.NewBufferFromBytes([]byte("should-fail"))
 	defer failBuffer.Destroy()
 
 	err = vault.AddSecret(secretName, failBuffer, false)
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "already exists")
+	require.ErrorIs(t, err, ErrSecretExists)
 }
 
 // TestVersionConcurrency tests concurrent version operations

internal/vault/path_traversal_test.go

@@ -41,10 +41,8 @@ func TestGetSecretVersionRejectsPathTraversal(t *testing.T) {
 			t.Parallel()
 
 			_, err := vlt.GetSecretVersion(name, "")
-			require.Error(t, err,
+			require.ErrorIs(t, err, vault.ErrInvalidSecretName,
 				"GetSecretVersion should reject malicious name: %s", name)
-			require.Contains(t, err.Error(), "invalid secret name",
-				"error should indicate invalid name for: %s", name)
 		})
 	}
 }
@@ -61,8 +59,7 @@ func TestGetSecretRejectsPathTraversal(t *testing.T) {
 	require.NoError(t, err)
 
 	_, err = vlt.GetSecret("../../../etc/passwd")
-	require.Error(t, err)
-	require.Contains(t, err.Error(), "invalid secret name")
+	require.ErrorIs(t, err, vault.ErrInvalidSecretName)
 }
 
 // TestGetSecretObjectRejectsPathTraversal verifies GetSecretObject
@@ -87,8 +84,8 @@ func TestGetSecretObjectRejectsPathTraversal(t *testing.T) {
 			t.Parallel()
 
 			_, err := vlt.GetSecretObject(name)
-			require.Error(t, err, "GetSecretObject should reject: %s", name)
-			require.Contains(t, err.Error(), "invalid secret name")
+			require.ErrorIs(t, err, vault.ErrInvalidSecretName,
+				"GetSecretObject should reject: %s", name)
 		})
 	}
 }

internal/vault/secrets_version_test.go

@@ -143,8 +143,7 @@ func TestVaultAddSecretMultipleVersions(t *testing.T) {
 	defer failBuffer.Destroy()
 
 	err := vault.AddSecret(testSecretPath, failBuffer, false)
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "already exists")
+	require.ErrorIs(t, err, ErrSecretExists)
 
 	// Add with force - should create new version
 	addTestSecretToVault(t, vault, testSecretPath, []byte("version-2"), true)
@@ -309,8 +308,7 @@ func TestVaultGetNonExistentVersion(t *testing.T) {
 
 	// Try to get non-existent version
 	_, err := vault.GetSecretVersion(testSecretPath, "20991231.999")
-	require.Error(t, err)
-	assert.Contains(t, err.Error(), "not found")
+	require.ErrorIs(t, err, ErrVersionNotFound)
 }
 
 func TestUpdateVersionMetadata(t *testing.T) {

internal/vault/vault_error_test.go

@@ -1,6 +1,7 @@
 package vault_test
 
 import (
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -36,8 +37,8 @@ func TestAddSecretFailsWithMissingPublicKey(t *testing.T) {
 	defer value.Destroy()
 
 	err := vlt.AddSecret(testSecretName, value, false)
-	require.Error(t, err, "AddSecret should fail when public key is missing")
-	assert.Contains(t, err.Error(), "failed to read long-term public key")
+	require.ErrorIs(t, err, os.ErrNotExist,
+		"AddSecret should fail when public key is missing")
 
 	// Verify that the secret directory was NOT created
 	secretDir := filepath.Join(vaultDir, "secrets.d", testSecretName)

pkg/agehd/agehd_test.go

@@ -38,7 +38,6 @@ const (
 	testMessageLargePattern  = "A"
 
 	// Error messages for validation
-	errorMsgNeed32Bytes = "need 32-byte scalar, got"
 	errorMsgInvalidXPRV = "invalid-xprv"
 
 	// Test constants for various scenarios
@@ -330,24 +329,17 @@ func TestClampFunction(t *testing.T) {
 	}
 }
 
-// requireIdentityError asserts that identity derivation failed with an
-// error containing errorMsg and returned no identity.
+// requireIdentityError asserts that identity derivation failed with
+// errInvalidScalarSize and returned no identity.
 func requireIdentityError(
 	t *testing.T,
 	identity *age.X25519Identity,
 	err error,
-	errorMsg string,
 ) {
 	t.Helper()
 
-	if err == nil {
-		t.Errorf("expected error but got none")
-	} else if !strings.Contains(err.Error(), errorMsg) {
-		t.Errorf(
-			"expected error containing %q, got %q",
-			errorMsg,
-			err.Error(),
-		)
+	if !errors.Is(err, errInvalidScalarSize) {
+		t.Errorf("expected errInvalidScalarSize, got %v", err)
 	}
 
 	if identity != nil {
@@ -363,31 +355,26 @@ func TestIdentityFromEntropyEdgeCases(t *testing.T) {
 		name        string
 		entropy     []byte
 		expectError bool
-		errorMsg    string
 	}{
 		{
 			name:        "nil entropy",
 			entropy:     nil,
 			expectError: true,
-			errorMsg:    errorMsgNeed32Bytes + " 0",
 		},
 		{
 			name:        "empty entropy",
 			entropy:     []byte{},
 			expectError: true,
-			errorMsg:    errorMsgNeed32Bytes + " 0",
 		},
 		{
 			name:        "too short entropy",
 			entropy:     make([]byte, 31),
 			expectError: true,
-			errorMsg:    errorMsgNeed32Bytes + " 31",
 		},
 		{
 			name:        "too long entropy",
 			entropy:     make([]byte, 33),
 			expectError: true,
-			errorMsg:    errorMsgNeed32Bytes + " 33",
 		},
 		{
 			name:        "valid 32-byte entropy",
@@ -419,7 +406,7 @@ func TestIdentityFromEntropyEdgeCases(t *testing.T) {
 			identity, err := IdentityFromEntropy(tt.entropy)
 
 			if tt.expectError {
-				requireIdentityError(t, identity, err, tt.errorMsg)
+				requireIdentityError(t, identity, err)
 
 				return
 			}

pkg/bip85/bip85_test.go

@@ -4,6 +4,7 @@ package bip85_test
 import (
 	"bytes"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"strings"
 	"testing"
@@ -1013,14 +1014,13 @@ func TestHexDerivation(t *testing.T) {
 func TestInvalidParameters(t *testing.T) {
 	t.Parallel()
 
-	logTestVector(t, "Invalid Parameters")
-
 	masterKey := mustParseTestMasterKey(t)
 
 	// Test cases for parameter validation
 	testCases := []struct {
 		name     string
 		testFunc func() error
+		want     error
 	}{
 		{
 			name: "BIP39 invalid word count",
@@ -1030,6 +1030,7 @@ func TestInvalidParameters(t *testing.T) {
 
 				return err
 			},
+			want: bip85.ErrInvalidWordCount,
 		},
 		{
 			name: "Base64 password too short",
@@ -1039,6 +1040,7 @@ func TestInvalidParameters(t *testing.T) {
 
 				return err
 			},
+			want: bip85.ErrInvalidBase64PwdLen,
 		},
 		{
 			name: "Base64 password too long",
@@ -1048,6 +1050,7 @@ func TestInvalidParameters(t *testing.T) {
 
 				return err
 			},
+			want: bip85.ErrInvalidBase64PwdLen,
 		},
 		{
 			name: "Base85 password too short",
@@ -1057,6 +1060,7 @@ func TestInvalidParameters(t *testing.T) {
 
 				return err
 			},
+			want: bip85.ErrInvalidBase85PwdLen,
 		},
 		{
 			name: "Base85 password too long",
@@ -1066,6 +1070,7 @@ func TestInvalidParameters(t *testing.T) {
 
 				return err
 			},
+			want: bip85.ErrInvalidBase85PwdLen,
 		},
 		{
 			name: "Hex data too small",
@@ -1075,6 +1080,7 @@ func TestInvalidParameters(t *testing.T) {
 
 				return err
 			},
+			want: bip85.ErrInvalidNumBytes,
 		},
 		{
 			name: "Hex data too large",
@@ -1084,23 +1090,43 @@ func TestInvalidParameters(t *testing.T) {
 
 				return err
 			},
+			want: bip85.ErrInvalidNumBytes,
 		},
 	}
 
 	// Run all validation test cases
 	for _, tc := range testCases {
-		t.Logf("Testing: %s", tc.name)
-
 		err := tc.testFunc()
-		if err == nil {
-			t.Errorf("Expected error for %s, but got nil", tc.name)
-		} else {
-			t.Logf("Got expected error: %v", err)
-			t.Logf("RESULT: PASS")
+		if !errors.Is(err, tc.want) {
+			t.Errorf("Expected %v for %s, got %v", tc.want, tc.name, err)
 		}
 	}
 }
 
+// TestDeriveBIP85EntropyErrors checks that DeriveBIP85Entropy returns
+// ErrNotPrivateKey for a public master key, and ErrInvalidPathComponent,
+// wrapped, for a path component that is not a number.
+func TestDeriveBIP85EntropyErrors(t *testing.T) {
+	t.Parallel()
+
+	masterKey := mustParseTestMasterKey(t)
+
+	publicKey, err := masterKey.Neuter()
+	if err != nil {
+		t.Fatalf("Failed to get the public key of the master key: %v", err)
+	}
+
+	_, err = bip85.DeriveBIP85Entropy(publicKey, testCase1Path)
+	if !errors.Is(err, bip85.ErrNotPrivateKey) {
+		t.Errorf("Expected ErrNotPrivateKey, got %v", err)
+	}
+
+	_, err = bip85.DeriveBIP85Entropy(masterKey, bip85.BIP85_MASTER_PATH+"/x'")
+	if !errors.Is(err, bip85.ErrInvalidPathComponent) {
+		t.Errorf("Expected ErrInvalidPathComponent, got %v", err)
+	}
+}
+
 // TestAdditionalDeriveHex tests additional hex derivation scenarios
 func TestAdditionalDeriveHex(t *testing.T) {
 	t.Parallel()