add state an context tests

Make sure duplicate depends_on entries are pruned from existing states
on read.

Make sure new state built from configs with multiple references to the
same resource only add it once to the Dependencies.

terraform/context_apply_test.go

@@ -8100,3 +8100,32 @@ func TestContext2Apply_terraformEnv(t *testing.T) {
 		t.Fatalf("bad: \n%s", actual)
 	}
 }
+
+// verify that multiple config references only create a single depends_on entry
+func TestContext2Apply_multiRef(t *testing.T) {
+	m := testModule(t, "apply-multi-ref")
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	if _, err := ctx.Plan(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	deps := state.Modules[0].Resources["aws_instance.other"].Dependencies
+	if len(deps) > 1 || deps[0] != "aws_instance.create" {
+		t.Fatalf("expected 1 depends_on entry for aws_instance.create, got %q", deps)
+	}
+}

terraform/state_test.go

@@ -1898,6 +1898,62 @@ func TestReadState_prune(t *testing.T) {
 	}
 }
 
+func TestReadState_pruneDependencies(t *testing.T) {
+	state := &State{
+		Serial:  9,
+		Lineage: "5d1ad1a1-4027-4665-a908-dbe6adff11d8",
+		Remote: &RemoteState{
+			Type: "http",
+			Config: map[string]string{
+				"url": "http://my-cool-server.com/",
+			},
+		},
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Dependencies: []string{
+					"aws_instance.bar",
+					"aws_instance.bar",
+				},
+				Resources: map[string]*ResourceState{
+					"foo": &ResourceState{
+						Dependencies: []string{
+							"aws_instance.baz",
+							"aws_instance.baz",
+						},
+						Primary: &InstanceState{
+							ID: "bar",
+						},
+					},
+				},
+			},
+		},
+	}
+	state.init()
+
+	buf := new(bytes.Buffer)
+	if err := WriteState(state, buf); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual, err := ReadState(buf)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	// make sure the duplicate Dependencies are filtered
+	modDeps := actual.Modules[0].Dependencies
+	resourceDeps := actual.Modules[0].Resources["foo"].Dependencies
+
+	if len(modDeps) > 1 || modDeps[0] != "aws_instance.bar" {
+		t.Fatalf("expected 1 module depends_on entry, got %q", modDeps)
+	}
+
+	if len(resourceDeps) > 1 || resourceDeps[0] != "aws_instance.baz" {
+		t.Fatalf("expected 1 resource depends_on entry, got  %q", resourceDeps)
+	}
+}
+
 func TestResourceNameSort(t *testing.T) {
 	names := []string{
 		"a",

terraform/test-fixtures/apply-multi-ref/main.tf

@@ -0,0 +1,8 @@
+resource "aws_instance" "create" {
+	bar = "abc"
+}
+
+resource "aws_instance" "other" {
+	var = "${aws_instance.create.id}"
+    foo = "${aws_instance.create.bar}"
+}