Support testing of configurations in JSON syntax.

This implements the proposal described in hashicorp#721

CHANGELOG.md

@@ -1,3 +1,7 @@
+ENHANCEMENTS
+
+* `helper/resource.TestStep` now has a `ConfigIsJSON` bool flag that allows tests to use configuration in the JSON syntax. ([#721](https://github.com/hashicorp/terraform-plugin-sdk/issues/721))
+
 # 2.4.4 (February 24, 2021)
 
 NOTES

helper/resource/testing.go

@@ -398,7 +398,11 @@ type TestStep struct {
 	// Config a string of the configuration to give to Terraform. If this
 	// is set, then the TestCase will execute this step with the same logic
 	// as a `terraform apply`.
-	Config string
+	//
+	// ConfigIsJSON, if true, will assume that the configuration in Config,
+	// if any, uses the JSON syntax rather than the native syntax.
+	Config       string
+	ConfigIsJSON bool
 
 	// Check is called after the Config is applied. Use this step to
 	// make your own API calls to check the status of things, and to

helper/resource/testing_new.go

@@ -72,6 +72,7 @@ func runNewTest(t testing.T, c TestCase, helper *plugintest.Helper) {
 		t.Fatal(err)
 	}
 
+	wd.SetConfigIsJSON(false)
 	err = wd.SetConfig(providerCfg)
 	if err != nil {
 		t.Fatalf("Error setting test config: %s", err)
@@ -196,11 +197,13 @@ func testIDRefresh(c TestCase, t testing.T, wd *plugintest.WorkingDir, step Test
 	if err != nil {
 		return err
 	}
+	wd.SetConfigIsJSON(false)
 	err = wd.SetConfig(cfg)
 	if err != nil {
 		t.Fatalf("Error setting import test config: %s", err)
 	}
 	defer func() {
+		wd.SetConfigIsJSON(step.ConfigIsJSON)
 		err = wd.SetConfig(step.Config)
 		if err != nil {
 			t.Fatalf("Error resetting test config: %s", err)

helper/resource/testing_new_config.go

@@ -35,6 +35,7 @@ func testStepNewConfig(t testing.T, c TestCase, wd *plugintest.WorkingDir, step
 		}
 	}
 
+	wd.SetConfigIsJSON(step.ConfigIsJSON)
 	err := wd.SetConfig(step.Config)
 	if err != nil {
 		return fmt.Errorf("Error setting config: %w", err)

helper/resource/testing_new_import_state.go

@@ -64,6 +64,7 @@ func testStepNewImportState(t testing.T, c TestCase, helper *plugintest.Helper,
 	}
 	importWd := helper.RequireNewWorkingDir(t)
 	defer importWd.Close()
+	importWd.SetConfigIsJSON(step.ConfigIsJSON)
 	err = importWd.SetConfig(step.Config)
 	if err != nil {
 		t.Fatalf("Error setting test config: %s", err)

internal/plugintest/working_dir.go

@@ -14,8 +14,9 @@ import (
 )
 
 const (
-	ConfigFileName = "terraform_plugin_test.tf"
-	PlanFileName   = "tfplan"
+	ConfigFileNameNative = "terraform_plugin_test.tf"
+	ConfigFileNameJSON   = ConfigFileNameNative + ".json"
+	PlanFileName         = "tfplan"
 )
 
 // WorkingDir represents a distinct working directory that can be used for
@@ -42,6 +43,11 @@ type WorkingDir struct {
 	reattachInfo tfexec.ReattachInfo
 
 	env map[string]string
+
+	// configIsJSON is a flag that affects the assumed syntax of the
+	// configuration passed to SetConfig. If true, SetConfig assumes the
+	// configuration is in the JSON syntax rather than the native syntax.
+	configIsJSON bool
 }
 
 // Close deletes the directories and files created to represent the receiving
@@ -77,14 +83,26 @@ func (wd *WorkingDir) GetHelper() *Helper {
 	return wd.h
 }
 
+// SetConfigIsJSON sets the configIsJSON flag, which affects all subsequent
+// calls to SetConfig.
+func (wd *WorkingDir) SetConfigIsJSON(configIsJSON bool) {
+	wd.configIsJSON = configIsJSON
+}
+
 // SetConfig sets a new configuration for the working directory.
 //
 // This must be called at least once before any call to Init, Plan, Apply, or
 // Destroy to establish the configuration. Any previously-set configuration is
 // discarded and any saved plan is cleared.
+//
+// The assumed syntax of the configuration can be changed by calling
+// SetConfigIsJSON prior to calling SetConfig.
 func (wd *WorkingDir) SetConfig(cfg string) error {
-	configFilename := filepath.Join(wd.baseDir, ConfigFileName)
-	err := ioutil.WriteFile(configFilename, []byte(cfg), 0700)
+	err := os.Remove(wd.configFilename(!wd.configIsJSON))
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	err = ioutil.WriteFile(wd.configFilename(wd.configIsJSON), []byte(cfg), 0700)
 	if err != nil {
 		return err
 	}
@@ -135,15 +153,19 @@ func (wd *WorkingDir) ClearPlan() error {
 // Init runs "terraform init" for the given working directory, forcing Terraform
 // to use the current version of the plugin under test.
 func (wd *WorkingDir) Init() error {
-	if _, err := os.Stat(wd.configFilename()); err != nil {
+	if _, err := os.Stat(wd.configFilename(wd.configIsJSON)); err != nil {
 		return fmt.Errorf("must call SetConfig before Init")
 	}
 
 	return wd.tf.Init(context.Background(), tfexec.Reattach(wd.reattachInfo))
 }
 
-func (wd *WorkingDir) configFilename() string {
-	return filepath.Join(wd.baseDir, ConfigFileName)
+func (wd *WorkingDir) configFilename(configIsJson bool) string {
+	if configIsJson {
+		return filepath.Join(wd.baseDir, ConfigFileNameJSON)
+	} else {
+		return filepath.Join(wd.baseDir, ConfigFileNameNative)
+	}
 }
 
 func (wd *WorkingDir) planFilename() string {