test: make must succeed/fail gadgets functions

For consistency with other gadgets like Grep, we make the MustSucceed
and MustFail gadgets private with a function to return an instance of
it.

test/gadgets_test.go

@@ -54,15 +54,23 @@ func InferName(c Checker) string {
 	return retVals[0].String()
 }
 
-type MustSucceed struct{}
+func MustSucceed() Checker {
+	return mustSucceed{}
+}
+
+type mustSucceed struct{}
 
-func (_ MustSucceed) Check(stdout, stderr string, err error) error {
+func (_ mustSucceed) Check(stdout, stderr string, err error) error {
 	return err
 }
 
-type MustFail struct{}
+func MustFail() Checker {
+	return mustFail{}
+}
+
+type mustFail struct{}
 
-func (_ MustFail) Check(stdout, stderr string, err error) error {
+func (_ mustFail) Check(stdout, stderr string, err error) error {
 	if err == nil {
 		return fmt.Errorf("unexpected command success")
 	}

test/install_test.go

@@ -7,19 +7,19 @@ func (ts *PackerTestSuite) TestInstallPluginWithMetadata() {
 	ts.Run("metadata plugin installed must not have metadata in its path", func() {
 		ts.PackerCommand().UsePluginDir(tempPluginDir).
 			SetArgs("plugins", "installed").
-			Assert(ts.T(), MustSucceed{}, Grep("packer-plugin-tester_v1.0.0[^+]", grepStdout))
+			Assert(ts.T(), MustSucceed(), Grep("packer-plugin-tester_v1.0.0[^+]", grepStdout))
 	})
 
 	ts.Run("plugin with metadata should work with validate", func() {
 		ts.PackerCommand().UsePluginDir(tempPluginDir).
 			SetArgs("validate", "./templates/simple.pkr.hcl").
-			Assert(ts.T(), MustSucceed{}, Grep("packer-plugin-tester_v1.0.0[^+][^\\n]+plugin:", grepStderr))
+			Assert(ts.T(), MustSucceed(), Grep("packer-plugin-tester_v1.0.0[^+][^\\n]+plugin:", grepStderr))
 	})
 
 	ts.Run("plugin with metadata should work with build", func() {
 		ts.PackerCommand().UsePluginDir(tempPluginDir).
 			SetArgs("build", "./templates/simple.pkr.hcl").
-			Assert(ts.T(), MustSucceed{}, Grep("packer-plugin-tester_v1.0.0[^+][^\\n]+plugin:", grepStderr))
+			Assert(ts.T(), MustSucceed(), Grep("packer-plugin-tester_v1.0.0[^+][^\\n]+plugin:", grepStderr))
 	})
 }
 
@@ -32,6 +32,6 @@ func (ts *PackerTestSuite) TestInstallPluginPrerelease() {
 	ts.Run("try install plugin with alpha1 prerelease - should fail", func() {
 		ts.PackerCommand().UsePluginDir(pluginDir).
 			SetArgs("plugins", "install", "--path", pluginPath, "github.com/hashicorp/tester").
-			Assert(ts.T(), MustFail{}, Grep("Packer can only install plugin releases with this command", grepStdout))
+			Assert(ts.T(), MustFail(), Grep("Packer can only install plugin releases with this command", grepStdout))
 	})
 }

test/loading_test.go

@@ -43,7 +43,7 @@ func (ts *PackerTestSuite) TestLoadingOrder() {
 				ts.PackerCommand().
 					SetArgs(command, tt.templatePath).
 					UsePluginDir(pluginDir).
-					Assert(t, MustSucceed{}, Grep(tt.grepStr))
+					Assert(t, MustSucceed(), Grep(tt.grepStr))
 			})
 		}
 	}
@@ -60,7 +60,7 @@ func (ts *PackerTestSuite) TestLoadWithLegacyPluginName() {
 	ts.Run("multiple plugins installed: one with no version in path, one with qualified name. Should pick-up the qualified one only.", func() {
 		ts.PackerCommand().UsePluginDir(pluginDir).
 			SetArgs("build", "templates/simple.pkr.hcl").
-			Assert(ts.T(), MustSucceed{}, Grep("packer-plugin-tester_v1\\.0\\.0[^\\n]+ plugin:", grepStderr))
+			Assert(ts.T(), MustSucceed(), Grep("packer-plugin-tester_v1\\.0\\.0[^\\n]+ plugin:", grepStderr))
 	})
 }
 
@@ -77,7 +77,7 @@ func (ts *PackerTestSuite) TestLoadWithSHAMismatches() {
 
 		ts.PackerCommand().UsePluginDir(pluginDir).
 			SetArgs("plugins", "installed").
-			Assert(ts.T(), MustSucceed{},
+			Assert(ts.T(), MustSucceed(),
 				Grep("packer-plugin-tester_v1\\.0\\.9[^\\n]+", grepStdout),
 				Grep("packer-plugin-tester_v1.0.10", grepStdout, grepInvert),
 				Grep("v1.0.10[^\\n]+ignoring possibly unsafe binary", grepStderr))
@@ -100,7 +100,7 @@ func (ts *PackerTestSuite) TestLoadWithSHAMismatches() {
 
 		ts.PackerCommand().UsePluginDir(pluginDir).
 			SetArgs("plugins", "installed").
-			Assert(ts.T(), MustSucceed{},
+			Assert(ts.T(), MustSucceed(),
 				Grep("packer-plugin-tester_v1\\.0\\.9[^\\n]+", grepStdout),
 				Grep("packer-plugin-tester_v1.0.10", grepInvert, grepStdout),
 				Grep("v1.0.10[^\\n]+ignoring possibly unsafe binary", grepStderr),

test/plugin_test.go

@@ -193,7 +193,7 @@ func (ts *PackerTestSuite) MakePluginDir(pluginVersions ...string) (pluginTempDi
 			err = fmt.Errorf("failed to get path to version %q, was it compiled?", pluginVersion)
 		}
 		cmd := ts.PackerCommand().SetArgs("plugins", "install", "--path", path, "github.com/hashicorp/tester").AddEnv("PACKER_PLUGIN_PATH", pluginTempDir)
-		cmd.Assert(t, MustSucceed{})
+		cmd.Assert(t, MustSucceed())
 		out, stderr, cmdErr := cmd.Run()
 		if cmdErr != nil {
 			err = fmt.Errorf("failed to install tester plugin version %q: %s\nCommand stdout: %s\nCommand stderr: %s", pluginVersion, err, out, stderr)