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/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 +4,8 @@
 package secret
 
 import (
+	"os"
+	"path/filepath"
 	"testing"
 	"time"
 
@@ -106,6 +108,10 @@ 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")
+
+	var cause *os.PathError
+
+	require.ErrorAs(t, err, &cause)
+	require.ErrorIs(t, err, os.ErrNotExist)
+	assert.Equal(t, filepath.Join(dir, seLongtermFilename), cause.Path)
 }

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()