chore(tests): drop use of testify/mock.Mock.TestData (#1467)

Simplify tests in pkg/helm by replacing a use of
testify/mock.Mock.TestData with just direct storage in the MockHelm
object.

Why? I'm a maintainer of github.com/stretchr/testify/mock and we are
considering deprecating (and ultimately removing) the TestData method
because it brings the single requirement of dependency
github.com/stretchr/objx.Map.
See stretchr/testify#1752

Author: dolmen

pkg/helm/jsonnet_test.go

@@ -14,6 +14,7 @@ const kubeVersion = "1.18.0"
 
 type MockHelm struct {
 	mock.Mock
+	templateCommandArgs []string
 }
 
 // fulfill the Helm interface
@@ -34,7 +35,7 @@ func (m *MockHelm) Template(name, chart string, opts TemplateOpts) (manifest.Lis
 	// them
 	execHelm := &ExecHelm{}
 	cmdArgs := execHelm.templateCommandArgs(name, chart, opts)
-	m.TestData().Set("templateCommandArgs", cmdArgs)
+	m.templateCommandArgs = cmdArgs
 
 	return args.Get(0).(manifest.List), args.Error(1)
 }
@@ -88,7 +89,7 @@ func callNativeFunction(t *testing.T, expectedHelmTemplateOptions TemplateOpts,
 
 	helmMock.AssertExpectations(t)
 
-	return helmMock.TestData().Get("templateCommandArgs").StringSlice()
+	return helmMock.templateCommandArgs
 }
 
 // TestDefaultCommandineFlagsIncludeCrds tests that the includeCrds flag is set