[FAB-11217] Increase test coverage for signer.go

Increase test coverage to 93.8%.
And, fix error message to omit ":", because
errors.Wrap() concatenates messages with ":".

Change-Id: I37a21239286121638ccee1057aff2fffea8382f6
Signed-off-by: Daisuke IIZUKA <daisuke.iizuka.ag@hitachi.com>

Author: Daisuke IIZUKA

cmd/common/signer/signer.go

@@ -79,11 +79,11 @@ func loadPrivateKey(file string) (*ecdsa.PrivateKey, error) {
 	}
 	bl, _ := pem.Decode(b)
 	if bl == nil {
-		return nil, errors.Errorf("%s: wrong PEM encoding", file)
+		return nil, errors.Errorf("failed to decode PEM block from %s", file)
 	}
 	key, err := x509.ParsePKCS8PrivateKey(bl.Bytes)
 	if err != nil {
-		return nil, errors.WithStack(err)
+		return nil, errors.Wrapf(err, "failed to parse private key from %s", file)
 	}
 	return key.(*ecdsa.PrivateKey), nil
 }

cmd/common/signer/signer_test.go

@@ -41,7 +41,7 @@ func TestSignerBadConfig(t *testing.T) {
 	}
 
 	signer, err := NewSigner(conf)
-	assert.Contains(t, err.Error(), "open testdata/signer/non_existent_cert: no such file or directory")
+	assert.EqualError(t, err, "open testdata/signer/non_existent_cert: no such file or directory")
 	assert.Nil(t, signer)
 
 	conf = Config{
@@ -51,7 +51,7 @@ func TestSignerBadConfig(t *testing.T) {
 	}
 
 	signer, err = NewSigner(conf)
-	assert.Contains(t, err.Error(), "open testdata/signer/non_existent_cert: no such file or directory")
+	assert.EqualError(t, err, "open testdata/signer/non_existent_cert: no such file or directory")
 	assert.Nil(t, signer)
 
 	conf = Config{
@@ -61,6 +61,16 @@ func TestSignerBadConfig(t *testing.T) {
 	}
 
 	signer, err = NewSigner(conf)
-	assert.Contains(t, err.Error(), "testdata/signer/broken_private_key: wrong PEM encoding")
+	assert.EqualError(t, err, "failed to decode PEM block from testdata/signer/broken_private_key")
+	assert.Nil(t, signer)
+
+	conf = Config{
+		MSPID:        "SampleOrg",
+		IdentityPath: filepath.Join("testdata", "signer", "cert.pem"),
+		KeyPath:      filepath.Join("testdata", "signer", "empty_private_key"),
+	}
+
+	signer, err = NewSigner(conf)
+	assert.EqualError(t, err, "failed to parse private key from testdata/signer/empty_private_key: asn1: syntax error: sequence truncated")
 	assert.Nil(t, signer)
 }

cmd/common/signer/testdata/signer/empty_private_key

@@ -0,0 +1,2 @@
+-----BEGIN PRIVATE KEY-----
+-----END PRIVATE KEY-----