Add SLSA verifier interface and mock implementation

- Define VerifierInterface for testable SLSA verification
- Implement MockVerifier with configurable behavior for testing
- Add helper functions for simulating verification scenarios
- Enable comprehensive testing of SLSA verification logic

Co-authored-by: Ona <[email protected]>

Author: leodido

pkg/leeway/cache/slsa/mock_verifier.go

@@ -0,0 +1,115 @@
+package slsa
+
+import (
+	"context"
+	"fmt"
+	"strings"
+)
+
+// MockVerifier implements VerifierInterface for testing
+type MockVerifier struct {
+	// VerifyFunc allows customizing verification behavior in tests
+	VerifyFunc func(ctx context.Context, artifactPath, attestationPath string) error
+	
+	// CallLog tracks verification calls for test assertions
+	CallLog []VerifyCall
+	
+	// DefaultResult controls the default verification result when VerifyFunc is nil
+	DefaultResult error
+}
+
+// VerifyCall represents a single verification call for testing
+type VerifyCall struct {
+	ArtifactPath    string
+	AttestationPath string
+	Context         context.Context
+}
+
+// NewMockVerifier creates a new mock verifier for testing
+func NewMockVerifier() *MockVerifier {
+	return &MockVerifier{
+		CallLog: make([]VerifyCall, 0),
+	}
+}
+
+// VerifyArtifact implements the VerifierInterface
+func (m *MockVerifier) VerifyArtifact(ctx context.Context, artifactPath, attestationPath string) error {
+	// Record the call for test assertions
+	m.CallLog = append(m.CallLog, VerifyCall{
+		ArtifactPath:    artifactPath,
+		AttestationPath: attestationPath,
+		Context:         ctx,
+	})
+	
+	// Use custom verification function if provided
+	if m.VerifyFunc != nil {
+		return m.VerifyFunc(ctx, artifactPath, attestationPath)
+	}
+	
+	// Return default result
+	return m.DefaultResult
+}
+
+// Reset clears the call log and resets the mock state
+func (m *MockVerifier) Reset() {
+	m.CallLog = make([]VerifyCall, 0)
+	m.VerifyFunc = nil
+	m.DefaultResult = nil
+}
+
+// SetVerifyResult sets a simple success/failure result for all verifications
+func (m *MockVerifier) SetVerifyResult(err error) {
+	m.DefaultResult = err
+}
+
+// SetVerifyFunc sets a custom verification function
+func (m *MockVerifier) SetVerifyFunc(fn func(ctx context.Context, artifactPath, attestationPath string) error) {
+	m.VerifyFunc = fn
+}
+
+// GetCallCount returns the number of verification calls made
+func (m *MockVerifier) GetCallCount() int {
+	return len(m.CallLog)
+}
+
+// GetLastCall returns the most recent verification call, or nil if no calls were made
+func (m *MockVerifier) GetLastCall() *VerifyCall {
+	if len(m.CallLog) == 0 {
+		return nil
+	}
+	return &m.CallLog[len(m.CallLog)-1]
+}
+
+// WasCalledWith checks if the verifier was called with specific paths
+func (m *MockVerifier) WasCalledWith(artifactPath, attestationPath string) bool {
+	for _, call := range m.CallLog {
+		if call.ArtifactPath == artifactPath && call.AttestationPath == attestationPath {
+			return true
+		}
+	}
+	return false
+}
+
+// SimulateVerificationFailure creates a verification function that fails for specific artifacts
+func SimulateVerificationFailure(failingArtifacts ...string) func(ctx context.Context, artifactPath, attestationPath string) error {
+	return func(ctx context.Context, artifactPath, attestationPath string) error {
+		for _, failing := range failingArtifacts {
+			if strings.Contains(artifactPath, failing) {
+				return fmt.Errorf("mock verification failed for artifact: %s", artifactPath)
+			}
+		}
+		return nil
+	}
+}
+
+// SimulateContextCancellation creates a verification function that respects context cancellation
+func SimulateContextCancellation() func(ctx context.Context, artifactPath, attestationPath string) error {
+	return func(ctx context.Context, artifactPath, attestationPath string) error {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		default:
+			return nil
+		}
+	}
+}

pkg/leeway/cache/slsa/verifier.go

@@ -11,6 +11,11 @@ import (
 	"github.com/slsa-framework/slsa-verifier/v2/options"
 )
 
+// VerifierInterface defines the interface for SLSA verification
+type VerifierInterface interface {
+	VerifyArtifact(ctx context.Context, artifactPath, attestationPath string) error
+}
+
 // Verifier handles SLSA attestation verification using Go API
 type Verifier struct {
 	sourceURI    string