Stateful Logic Testing

Problem

Complex state logic embedded in components becomes difficult to test thoroughly without rendering entire component trees. Reducers, selectors, or custom hooks contain business logic that needs comprehensive testing, but testing through UI interactions is slow and brittle.

Solution

Test complex state management logic independently from UI components. This makes tests faster and more focused on business logic.

Example

This demonstrates testing state management logic independently from UI components, making tests faster, more focused on business logic, and easier to maintain.

test('counter increments', () => {
  // Test hook logic without rendering full component tree
  const { result } = renderHook(() => useCounter());

  // Trigger state change
  act(() => {
    result.current.increment();
  });

  // Verify state update logic works correctly
  expect(result.current.count).toBe(1);
});

Benefits

• Makes tests faster by avoiding rendering entire component trees.
• Focuses tests on business logic rather than UI details.
• Enables thorough testing of edge cases and state transitions.
• Makes tests more maintainable since they’re decoupled from UI changes.

Tradeoffs

• Requires additional tools like renderHook for testing hooks.
• May miss integration issues between state logic and UI.
• Can create false confidence if UI integration isn’t tested separately.
• Needs careful consideration of what to test in isolation versus integration.