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

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()