Show diff when matching command output in tests for easier debugging.

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/Masterminds/goutils v1.1.0 // indirect
 	github.com/Masterminds/semver v1.4.2 // indirect
 	github.com/Masterminds/sprig v2.18.0+incompatible
+	github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883
 	github.com/blang/semver v3.5.1+incompatible
 	github.com/c-bata/go-prompt v0.2.4-0.20200321140817-d043be076398
 	github.com/cucumber/godog v0.12.2

go.sum

@@ -50,6 +50,8 @@ github.com/alcortesm/tgz v0.0.0-20161220082320-9c5fe88206d7 h1:uSoVVbwJiQipAclBb
 github.com/alcortesm/tgz v0.0.0-20161220082320-9c5fe88206d7/go.mod h1:6zEj6s6u/ghQa61ZWa/C2Aw3RkjiTBOix7dkqa1VLIs=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
+github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883 h1:bvNMNQO63//z+xNgfBlViaCIJKLlCJ6/fmUseuG0wVQ=
+github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883/go.mod h1:rCTlJbsFo29Kk6CurOXKm700vrz8f0KW0JNfpkRJY/8=
 github.com/anmitsu/go-shlex v0.0.0-20161002113705-648efa622239 h1:kFOfPq6dUM1hTo4JG6LR5AXSUEsOjtdm0kw0FtQtMJA=
 github.com/anmitsu/go-shlex v0.0.0-20161002113705-648efa622239/go.mod h1:2FmKhYUyUczH0OGQWaF5ceTx0UBShxjsH6f8oGKYe2c=
 github.com/antihax/optional v1.0.0/go.mod h1:uupD/76wgC+ih3iEmQUL+0Ugr19nfwCT1kdvxnR2qWY=

oya_test.go

@@ -11,6 +11,7 @@ import (
 	"runtime"
 	"strings"
 
+	"github.com/andreyvit/diff"
 	"github.com/cucumber/godog"
 	"github.com/pkg/errors"
 	log "github.com/sirupsen/logrus"
@@ -281,7 +282,8 @@ func (c *SuiteContext) theCommandFailsWithErrorMatching(errMsg *gherkin.DocStrin
 func (c *SuiteContext) theCommandOutputs(expected *gherkin.DocString) error {
 	actual := c.stdout.String()
 	if actual != expected.Content {
-		return fmt.Errorf("unexpected %v; expected: %q", actual, expected.Content)
+		return fmt.Errorf("unexpected %v; expected: %v; diff: %v",
+			actual, expected.Content, diff.LineDiff(actual, expected.Content))
 	}
 	return nil
 }
@@ -290,7 +292,7 @@ func (c *SuiteContext) theCommandOutputsTextMatching(expected *gherkin.DocString
 	actual := c.stdout.String()
 	rx := regexp.MustCompile(expected.Content)
 	if !rx.MatchString(actual) {
-		return fmt.Errorf("unexpected %v; expected to match: %q", actual, expected.Content)
+		return fmt.Errorf("unexpected %v; expected to match: %v", actual, expected.Content)
 	}
 	return nil
 }