protofsm: add generic type assertion to state machine tests

This commit introduces a new generic type assertion function
`assertState` to the state machine tests. This function asserts that the
state machine is currently in the expected state type and returns the
state cast to that type. This allows us to directly access the fields of
the state without having to perform a type assertion manually.

Author: Roasbeef

protofsm/state_machine_test.go

@@ -321,12 +321,20 @@ func (d *dummyStateSpent) IsTerminal() bool {
 	return true
 }
 
-func assertState[Event any, Env Environment](t *testing.T,
-	m *StateMachine[Event, Env], expectedState State[Event, Env]) {
+// assertState asserts that the state machine is currently in the expected
+// state type and returns the state cast to that type.
+func assertState[Event any, Env Environment, S State[Event, Env]](t *testing.T,
+	m *StateMachine[Event, Env], expectedState S) S {
 
 	state, err := m.CurrentState()
 	require.NoError(t, err)
 	require.IsType(t, expectedState, state)
+
+	// Perform the type assertion to return the concrete type.
+	concreteState, ok := state.(S)
+	require.True(t, ok, "state type assertion failed")
+
+	return concreteState
 }
 
 func assertStateTransitions[Event any, Env Environment](
@@ -639,18 +647,15 @@ func TestStateMachineConfMapper(t *testing.T) {
 	assertStateTransitions(t, stateSub, expectedStates)
 
 	// Final state assertion.
-	finalState, err := stateMachine.CurrentState()
-	require.NoError(t, err)
-	require.IsType(t, &dummyStateConfirmed{}, finalState)
+	finalState := assertState(t, &stateMachine, &dummyStateConfirmed{})
 
 	// Assert that the details from the confirmation event were correctly
 	// propagated to the final state.
-	finalStateDetails := finalState.(*dummyStateConfirmed)
 	require.Equal(t,
-		*simulatedConf.BlockHash, finalStateDetails.blockHash,
+		*simulatedConf.BlockHash, finalState.blockHash,
 	)
 	require.Equal(t,
-		simulatedConf.BlockHeight, finalStateDetails.blockHeight,
+		simulatedConf.BlockHeight, finalState.blockHeight,
 	)
 
 	adapters.AssertExpectations(t)
@@ -719,18 +724,15 @@ func TestStateMachineSpendMapper(t *testing.T) {
 	assertStateTransitions(t, stateSub, expectedStates)
 
 	// Final state assertion.
-	finalState, err := stateMachine.CurrentState()
-	require.NoError(t, err)
-	require.IsType(t, &dummyStateSpent{}, finalState)
+	finalState := assertState(t, &stateMachine, &dummyStateSpent{})
 
 	// Assert that the details from the spend event were correctly
 	// propagated to the final state.
-	finalStateDetails := finalState.(*dummyStateSpent)
 	require.Equal(t,
-		*simulatedSpend.SpenderTxHash, finalStateDetails.spenderTxHash,
+		*simulatedSpend.SpenderTxHash, finalState.spenderTxHash,
 	)
 	require.Equal(t,
-		simulatedSpend.SpendingHeight, finalStateDetails.spendingHeight,
+		simulatedSpend.SpendingHeight, finalState.spendingHeight,
 	)
 
 	adapters.AssertExpectations(t)