add tests for bad transitions with fsmnext

backend/controller/dal/fsm_integration_test.go

@@ -189,11 +189,15 @@ func TestFSMNext(t *testing.T) {
 		// Schedule next and then error and retry. Each error should be the expected error, not a failure to schedule the next state
 		transitionFSMWithOptions("3", 1, optional.Some("computers are fun"), "A", "B"),
 
+		// Bad progression
+		transitionFSM("4", "A", "B", "B"),
+
 		in.Sleep(4*time.Second),
 
 		checkAsyncCall("1", "A", "B", "C", "D"),
 		checkRepeatedAsyncCallError("2", "A", "fsm instance already has its next state set"),
 		// will get "fsm instance already has its next state set" if next event is not cleared properly
 		checkRepeatedAsyncCallError("3", "A", "computers are fun"),
+		checkRepeatedAsyncCallError("4", "B", `invalid event "fsmnext.EventB" for state "fsmnext.stateB"`),
 	)
 }

backend/controller/dal/testdata/go/fsmnext/fsmnext_test.go

@@ -34,3 +34,16 @@ func TestDoubleNext(t *testing.T) {
 		},
 	}).Error(), `fsm "fsm" instance "1" already has a pending event`)
 }
+
+func TestBadProgression(t *testing.T) {
+	// Simple progression through each state
+	ctx := ftltest.Context()
+
+	assert.EqualError(t, SendOne(ctx, Request{
+		State: A,
+		Event: Event{
+			Instance:   "1",
+			NextStates: []State{B, C, C},
+		},
+	}), `invalid event "fsmnext.EventC" for state "fsmnext.EventC"`)
+}