look for err specific to file write

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

pkg/cmd/attestation/download/download_test.go

@@ -310,5 +310,6 @@ func TestRunDownload(t *testing.T) {
 
 		err := runDownload(&opts)
 		require.Error(t, err)
+		require.ErrorAs(t, err, &ErrAttestationFileCreation)
 	})
 }

pkg/cmd/attestation/download/metadata.go

@@ -2,12 +2,15 @@ package download
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
 
 	"github.com/cli/cli/v2/pkg/cmd/attestation/api"
 )
 
+var ErrAttestationFileCreation = fmt.Errorf("failed to write attestations to file")
+
 type MetadataStore interface {
 	createMetadataFile(artifactDigest string, attestationsResp []*api.Attestation) (string, error)
 }
@@ -29,29 +32,29 @@ func (s *LiveStore) createMetadataFile(artifactDigest string, attestationsResp [
 
 	f, err := os.Create(metadataFilePath)
 	if err != nil {
-		return "", fmt.Errorf("failed to create trusted metadata file: %w", err)
+		return "", errors.Join(ErrAttestationFileCreation, fmt.Errorf("failed to create file: %w", err))
 	}
 
 	for _, resp := range attestationsResp {
 		bundle := resp.Bundle
 		attBytes, err := json.Marshal(bundle)
 		if err != nil {
-			return "", fmt.Errorf("failed to marshall attestation to JSON: %w", err)
+			return "", errors.Join(ErrAttestationFileCreation, fmt.Errorf("failed to marshall attestation to JSON while writing to file: %w", err))
 		}
 
 		withNewline := fmt.Sprintf("%s\n", attBytes)
 		_, err = f.Write([]byte(withNewline))
 		if err != nil {
 			if err = f.Close(); err != nil {
-				return "", fmt.Errorf("failed to close file while handling write error: %w", err)
+				return "", errors.Join(ErrAttestationFileCreation, fmt.Errorf("failed to close file while handling write error: %w", err))
 			}
 
-			return "", fmt.Errorf("failed to write trusted metadata: %w", err)
+			return "", errors.Join(ErrAttestationFileCreation, fmt.Errorf("failed to write attestations: %w", err))
 		}
 	}
 
 	if err = f.Close(); err != nil {
-		return "", fmt.Errorf("failed to close file after writing metadata: %w", err)
+		return "", errors.Join(ErrAttestationFileCreation, fmt.Errorf("failed to close file after writing attestations: %w", err))
 	}
 
 	return metadataFilePath, nil