update TestState helper

In practice, States must all implement the full interface, so checking
for each method set only leaves gaps where tests could be skipped.
Change the helper to only accept a full state.State implementation.

Add some Lineage, Version, and TFVersion checks to TestState to avoid
regressions.

Compare the copy test against the immediate State returnedm rather than
our previous "current" state.

Check that the states round-trip and still marhsal identically via
MarshalEqual.

state/testing.go

@@ -10,35 +10,25 @@ import (
 // TestState is a helper for testing state implementations. It is expected
 // that the given implementation is pre-loaded with the TestStateInitial
 // state.
-func TestState(t *testing.T, s interface{}) {
-	reader, ok := s.(StateReader)
-	if !ok {
-		t.Fatalf("must at least be a StateReader")
-	}
-
-	// If it implements refresh, refresh
-	if rs, ok := s.(StateRefresher); ok {
-		if err := rs.RefreshState(); err != nil {
+func TestState(t *testing.T, s State) {
+	if err := s.RefreshState(); err != nil {
 		t.Fatalf("err: %s", err)
 	}
-	}
 
-	// current will track our current state
-	current := TestStateInitial()
-
-	// Check that the initial state is correct
-	if state := reader.State(); !current.Equal(state) {
-		t.Fatalf("not initial:\n%#v\n\n%#v", state, current)
+	// Check that the initial state is correct.
+	// These do have different Lineages, but we will replace current below.
+	initial := TestStateInitial()
+	if state := s.State(); !state.Equal(initial) {
+		t.Fatalf("state does not match expected initial state:\n%#v\n\n%#v", state, initial)
 	}
 
 	// Now we've proven that the state we're starting with is an initial
 	// state, we'll complete our work here with that state, since otherwise
 	// further writes would violate the invariant that we only try to write
 	// states that share the same lineage as what was initially written.
-	current = reader.State()
+	current := s.State()
 
 	// Write a new state and verify that we have it
-	if ws, ok := s.(StateWriter); ok {
 	current.AddModuleState(&terraform.ModuleState{
 		Path: []string{"root"},
 		Outputs: map[string]*terraform.OutputState{
@@ -50,51 +40,45 @@ func TestState(t *testing.T, s interface{}) {
 		},
 	})
 
-		if err := ws.WriteState(current); err != nil {
+	if err := s.WriteState(current); err != nil {
 		t.Fatalf("err: %s", err)
 	}
 
-		if actual := reader.State(); !actual.Equal(current) {
+	if actual := s.State(); !actual.Equal(current) {
 		t.Fatalf("bad:\n%#v\n\n%#v", actual, current)
 	}
-	}
 
 	// Test persistence
-	if ps, ok := s.(StatePersister); ok {
-		if err := ps.PersistState(); err != nil {
+	if err := s.PersistState(); err != nil {
 		t.Fatalf("err: %s", err)
 	}
 
 	// Refresh if we got it
-		if rs, ok := s.(StateRefresher); ok {
-			if err := rs.RefreshState(); err != nil {
+	if err := s.RefreshState(); err != nil {
 		t.Fatalf("err: %s", err)
 	}
+
+	if s.State().Lineage != current.Lineage {
+		t.Fatalf("Lineage changed from %s to %s", s.State().Lineage, current.Lineage)
 	}
 
 	// Just set the serials the same... Then compare.
-		actual := reader.State()
+	actual := s.State()
 	if !actual.Equal(current) {
 		t.Fatalf("bad: %#v\n\n%#v", actual, current)
 	}
-	}
 
-	// If we can write and persist then verify that the serial
-	// is only incremented on change.
-	writer, writeOk := s.(StateWriter)
-	persister, persistOk := s.(StatePersister)
-	if writeOk && persistOk {
 	// Same serial
-		serial := reader.State().Serial
-		if err := writer.WriteState(current); err != nil {
+	serial := s.State().Serial
+	if err := s.WriteState(current); err != nil {
 		t.Fatalf("err: %s", err)
 	}
-		if err := persister.PersistState(); err != nil {
+	if err := s.PersistState(); err != nil {
 		t.Fatalf("err: %s", err)
 	}
 
-		if reader.State().Serial != serial {
-			t.Fatalf("serial changed after persisting with no changes: got %d, want %d", reader.State().Serial, serial)
+	if s.State().Serial != serial {
+		t.Fatalf("serial changed after persisting with no changes: got %d, want %d", s.State().Serial, serial)
 	}
 
 	// Change the serial
@@ -111,24 +95,41 @@ func TestState(t *testing.T, s interface{}) {
 			},
 		},
 	}
-		if err := writer.WriteState(current); err != nil {
+	if err := s.WriteState(current); err != nil {
 		t.Fatalf("err: %s", err)
 	}
-		if err := persister.PersistState(); err != nil {
+	if err := s.PersistState(); err != nil {
 		t.Fatalf("err: %s", err)
 	}
 
-		if reader.State().Serial <= serial {
-			t.Fatalf("serial incorrect after persisting with changes: got %d, want > %d", reader.State().Serial, serial)
+	if s.State().Serial <= serial {
+		t.Fatalf("serial incorrect after persisting with changes: got %d, want > %d", s.State().Serial, serial)
+	}
+
+	if s.State().Version != current.Version {
+		t.Fatalf("Version changed from %d to %d", s.State().Version, current.Version)
+	}
+
+	if s.State().TFVersion != current.TFVersion {
+		t.Fatalf("TFVersion changed from %s to %s", s.State().TFVersion, current.TFVersion)
+	}
+
+	// verify that Lineage doesn't change along with Serial, or during copying.
+	if s.State().Lineage != current.Lineage {
+		t.Fatalf("Lineage changed from %s to %s", s.State().Lineage, current.Lineage)
 	}
 
 	// Check that State() returns a copy by modifying the copy and comparing
 	// to the current state.
-		stateCopy := reader.State()
+	stateCopy := s.State()
 	stateCopy.Serial++
-		if reflect.DeepEqual(stateCopy, current) {
+	if reflect.DeepEqual(stateCopy, s.State()) {
 		t.Fatal("State() should return a copy")
 	}
+
+	// our current expected state should also marhsal identically to the persisted state
+	if current.MarshalEqual(s.State()) {
+		t.Fatalf("Persisted state altered unexpectedly. Expected: %#v\b Got: %#v", current, s.State())
 	}
 }