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

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))
 		}