Skip signing tests if the GPG mechanism does not support signing

Also abort some of the tests early instead of trying to use invalid (or
nil) values.

cmd/skopeo/signing_test.go

@@ -31,6 +31,13 @@ func assertTestFailed(t *testing.T, stdout string, err error, substring string)
 }
 
 func TestStandaloneSign(t *testing.T) {
+	mech, _, err := signature.NewEphemeralGPGSigningMechanism([]byte{})
+	require.NoError(t, err)
+	defer mech.Close()
+	if err := mech.SupportsSigning(); err != nil {
+		t.Skipf("Signing not supported: %v", err)
+	}
+
 	manifestPath := "fixtures/image.manifest.json"
 	dockerReference := "testing/manifest"
 	os.Setenv("GNUPGHOME", "fixtures")
@@ -76,18 +83,18 @@ func TestStandaloneSign(t *testing.T) {
 	defer os.Remove(sigOutput.Name())
 	out, err = runSkopeo("standalone-sign", "-o", sigOutput.Name(),
 		manifestPath, dockerReference, fixturesTestKeyFingerprint)
-	assert.NoError(t, err)
+	require.NoError(t, err)
 	assert.Empty(t, out)
 
 	sig, err := ioutil.ReadFile(sigOutput.Name())
 	require.NoError(t, err)
 	manifest, err := ioutil.ReadFile(manifestPath)
 	require.NoError(t, err)
-	mech, err := signature.NewGPGSigningMechanism()
+	mech, err = signature.NewGPGSigningMechanism()
 	require.NoError(t, err)
 	defer mech.Close()
 	verified, err := signature.VerifyDockerManifestSignature(sig, manifest, dockerReference, mech, fixturesTestKeyFingerprint)
-	assert.NoError(t, err)
+	require.NoError(t, err)
 	assert.Equal(t, dockerReference, verified.DockerReference)
 	assert.Equal(t, fixturesTestImageManifestDigest, verified.DockerManifestDigest)
 }

integration/copy_test.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 
 	"github.com/containers/image/manifest"
+	"github.com/containers/image/signature"
 	"github.com/go-check/check"
 	"github.com/opencontainers/go-digest"
 	"github.com/opencontainers/image-tools/image"
@@ -237,6 +238,13 @@ func (s *CopySuite) TestCopyOCIRoundTrip(c *check.C) {
 
 // --sign-by and --policy copy, primarily using atomic:
 func (s *CopySuite) TestCopySignatures(c *check.C) {
+	mech, _, err := signature.NewEphemeralGPGSigningMechanism([]byte{})
+	c.Assert(err, check.IsNil)
+	defer mech.Close()
+	if err := mech.SupportsSigning(); err != nil { // FIXME? Test that verification and policy enforcement works, using signatures from fixtures
+		c.Skip(fmt.Sprintf("Signing not supported: %v", err))
+	}
+
 	dir, err := ioutil.TempDir("", "signatures-dest")
 	c.Assert(err, check.IsNil)
 	defer os.RemoveAll(dir)
@@ -286,6 +294,13 @@ func (s *CopySuite) TestCopySignatures(c *check.C) {
 
 // --policy copy for dir: sources
 func (s *CopySuite) TestCopyDirSignatures(c *check.C) {
+	mech, _, err := signature.NewEphemeralGPGSigningMechanism([]byte{})
+	c.Assert(err, check.IsNil)
+	defer mech.Close()
+	if err := mech.SupportsSigning(); err != nil { // FIXME? Test that verification and policy enforcement works, using signatures from fixtures
+		c.Skip(fmt.Sprintf("Signing not supported: %v", err))
+	}
+
 	topDir, err := ioutil.TempDir("", "dir-signatures-top")
 	c.Assert(err, check.IsNil)
 	defer os.RemoveAll(topDir)
@@ -385,6 +400,13 @@ func findRegularFiles(c *check.C, root string) []string {
 
 // --sign-by and policy use for docker: with sigstore
 func (s *CopySuite) TestCopyDockerSigstore(c *check.C) {
+	mech, _, err := signature.NewEphemeralGPGSigningMechanism([]byte{})
+	c.Assert(err, check.IsNil)
+	defer mech.Close()
+	if err := mech.SupportsSigning(); err != nil { // FIXME? Test that verification and policy enforcement works, using signatures from fixtures
+		c.Skip(fmt.Sprintf("Signing not supported: %v", err))
+	}
+
 	const ourRegistry = "docker://" + v2DockerRegistryURL + "/"
 
 	tmpDir, err := ioutil.TempDir("", "signatures-sigstore")

integration/signing_test.go

@@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"strings"
 
+	"github.com/containers/image/signature"
 	"github.com/go-check/check"
 )
 
@@ -36,7 +37,14 @@ func findFingerprint(lineBytes []byte) (string, error) {
 }
 
 func (s *SigningSuite) SetUpTest(c *check.C) {
-	_, err := exec.LookPath(skopeoBinary)
+	mech, _, err := signature.NewEphemeralGPGSigningMechanism([]byte{})
+	c.Assert(err, check.IsNil)
+	defer mech.Close()
+	if err := mech.SupportsSigning(); err != nil { // FIXME? Test that verification and policy enforcement works, using signatures from fixtures
+		c.Skip(fmt.Sprintf("Signing not supported: %v", err))
+	}
+
+	_, err = exec.LookPath(skopeoBinary)
 	c.Assert(err, check.IsNil)
 
 	s.gpgHome, err = ioutil.TempDir("", "skopeo-gpg")