terraform: test to ensure data sources work on Apply operation

It appears data sources have always been coded to work during apply, as
can be verified with this test (no impl. changes were necessary to make
it pass).

This test should be added to ensure our apply graph always works with
data sources as well.

terraform/context_apply_test.go

@@ -508,6 +508,38 @@ func TestContext2Apply_destroyComputed(t *testing.T) {
 	}
 }
 
+func TestContext2Apply_dataBasic(t *testing.T) {
+	m := testModule(t, "apply-data-basic")
+	p := testProvider("null")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	p.ReadDataApplyReturn = &InstanceState{ID: "yo"}
+
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"null": testProviderFuncFixed(p),
+		},
+	})
+
+	if p, err := ctx.Plan(); err != nil {
+		t.Fatalf("err: %s", err)
+	} else {
+		t.Logf(p.String())
+	}
+
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyDataBasicStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s", actual)
+	}
+}
+
 func TestContext2Apply_destroyData(t *testing.T) {
 	m := testModule(t, "apply-destroy-data-resource")
 	p := testProvider("null")

terraform/terraform_test.go

@@ -25,13 +25,13 @@ func TestMain(m *testing.M) {
 	// Experimental features
 	xNewApply := flag.Bool("Xnew-apply", false, "Experiment: new apply graph")
 
+	// Normal features
+	shadow := flag.Bool("shadow", true, "Enable shadow graph")
+
 	flag.Parse()
 
 	// Setup experimental features
 	X_newApply = *xNewApply
-	if X_newApply {
-		println("Xnew-apply enabled")
-	}
 
 	if testing.Verbose() {
 		// if we're verbose, use the logging requested by TF_LOG
@@ -48,7 +48,7 @@ func TestMain(m *testing.M) {
 	contextTestDeepCopyOnPlan = true
 
 	// Shadow the new graphs
-	contextTestShadow = true
+	contextTestShadow = *shadow
 
 	os.Exit(m.Run())
 }
@@ -257,6 +257,11 @@ aws_instance.foo:
   type = aws_instance
 `
 
+const testTerraformApplyDataBasicStr = `
+data.null_data_source.testing:
+  ID = yo
+`
+
 const testTerraformApplyRefCountStr = `
 aws_instance.bar:
   ID = foo

terraform/test-fixtures/apply-data-basic/main.tf

@@ -0,0 +1 @@
+data "null_data_source" "testing" {}