Revert "revert: rego evaluator result" (#15)

This reverts commit 0126ba9a0b.

internal/test/test.go

@@ -18,6 +18,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/v1/layout"
 	"github.com/google/go-containerregistry/pkg/v1/partial"
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
+	"github.com/open-policy-agent/opa/rego"
 	"github.com/secure-systems-lab/go-securesystemslib/dsse"
 )
 
@@ -87,20 +88,33 @@ func GetMockSigner(ctx context.Context) (dsse.SignerVerifier, error) {
 }
 
 type MockPolicyEvaluator struct {
-	EvaluateFunc func(ctx context.Context, resolver oci.AttestationResolver, policy []*policy.PolicyFile, input *policy.PolicyInput) error
+	EvaluateFunc func(ctx context.Context, resolver oci.AttestationResolver, policy []*policy.PolicyFile, input *policy.PolicyInput) (*rego.ResultSet, error)
 }
 
-func (pe *MockPolicyEvaluator) Evaluate(ctx context.Context, resolver oci.AttestationResolver, policy []*policy.PolicyFile, input *policy.PolicyInput) error {
+func (pe *MockPolicyEvaluator) Evaluate(ctx context.Context, resolver oci.AttestationResolver, policy []*policy.PolicyFile, input *policy.PolicyInput) (*rego.ResultSet, error) {
 	if pe.EvaluateFunc != nil {
 		return pe.EvaluateFunc(ctx, resolver, policy, input)
 	}
-	return nil
+	return AllowedResult(), nil
 }
 
 func GetMockPolicy() policy.PolicyEvaluator {
 	return &MockPolicyEvaluator{
-		EvaluateFunc: func(ctx context.Context, resolver oci.AttestationResolver, policy []*policy.PolicyFile, input *policy.PolicyInput) error {
-			return nil
+		EvaluateFunc: func(ctx context.Context, resolver oci.AttestationResolver, pfs []*policy.PolicyFile, input *policy.PolicyInput) (*rego.ResultSet, error) {
+			return AllowedResult(), nil
+		},
+	}
+}
+
+func AllowedResult() *rego.ResultSet {
+	return &rego.ResultSet{
+		{
+			Bindings: rego.Vars{},
+			Expressions: []*rego.ExpressionValue{
+				{
+					Value: true,
+				},
+			},
 		},
 	}
 }