add missing nil struct checks and udpate error messages

Signed-off-by: Meredith Lancaster <malancas@github.com>

pkg/cmd/attestation/api/mock_client.go

@@ -31,9 +31,9 @@ func OnGetByDigestSuccess(params FetchParams) ([]*Attestation, error) {
 
 func OnGetByDigestFailure(params FetchParams) ([]*Attestation, error) {
 	if params.Repo != "" {
-		return nil, fmt.Errorf("failed to fetch by repo and digest")
+		return nil, fmt.Errorf("failed to fetch attestations from %s", params.Repo)
 	}
-	return nil, fmt.Errorf("failed to fetch by owner and digest")
+	return nil, fmt.Errorf("failed to fetch attestations from %s", params.Owner)
 }
 
 func NewTestClient() *MockClient {

pkg/cmd/attestation/verification/attestation_test.go

@@ -162,6 +162,6 @@ func TestFilterAttestations(t *testing.T) {
 	require.NoError(t, err)
 
 	filtered, err = FilterAttestations("NonExistentPredicate", attestations)
-	require.Len(t, filtered, 0)
-	require.NoError(t, err)
+	require.Nil(t, filtered)
+	require.Error(t, err)
 }

pkg/cmd/attestation/verify/attestation.go

@@ -1,6 +1,7 @@
 package verify
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/cli/cli/v2/internal/text"
@@ -13,6 +14,11 @@ func getAttestations(o *Options, a artifact.DigestedArtifact) ([]*api.Attestatio
 	// Fetch attestations from GitHub API within this if block since predicate type
 	// filter is done when the API is called
 	if o.FetchAttestationsFromGitHubAPI() {
+		if o.APIClient == nil {
+			errMsg := "✗ No APIClient provided"
+			return nil, errMsg, errors.New(errMsg)
+		}
+
 		params := api.FetchParams{
 			Digest:        a.DigestWithAlg(),
 			Limit:         o.Limit,

pkg/cmd/attestation/verify/verify_test.go

@@ -510,7 +510,7 @@ func TestRunVerify(t *testing.T) {
 
 		err := runVerify(&customOpts)
 		require.Error(t, err)
-		require.ErrorContains(t, err, "no matching predicate found")
+		require.ErrorContains(t, err, "no attestations found with predicate type")
 	})
 
 	t.Run("with valid OCI artifact with UseBundleFromRegistry flag but no bundle return from registry", func(t *testing.T) {