First bunch of tests for lifecycle hooks blocks (#574)

* Add tests for useMount hook

* Add tests for useUnmount hook

* Add tests for useEffectOnce hook

src/__tests__/useEffectOnce.test.ts

@@ -0,0 +1,21 @@
+import { renderHook } from '@testing-library/react-hooks';
+import { useEffectOnce } from '..';
+
+const mockEffectCleanup = jest.fn();
+const mockEffectCallback = jest.fn().mockReturnValue(mockEffectCleanup);
+
+it('should run provided effect only once', () => {
+  const { rerender } = renderHook(() => useEffectOnce(mockEffectCallback));
+  expect(mockEffectCallback).toHaveBeenCalledTimes(1);
+
+  rerender();
+  expect(mockEffectCallback).toHaveBeenCalledTimes(1);
+});
+
+it('should run clean-up provided on unmount', () => {
+  const { unmount } = renderHook(() => useEffectOnce(mockEffectCallback));
+  expect(mockEffectCleanup).not.toHaveBeenCalled();
+
+  unmount();
+  expect(mockEffectCleanup).toHaveBeenCalledTimes(1);
+});

src/__tests__/useMount.test.ts

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+import { renderHook } from '@testing-library/react-hooks';
+import { useMount } from '..';
+
+const mockCallback = jest.fn();
+
+afterEach(() => {
+  jest.resetAllMocks();
+});
+
+it('should call provided callback on mount', () => {
+  renderHook(() => useMount(mockCallback));
+
+  expect(mockCallback).toHaveBeenCalledTimes(1);
+});
+
+it('should not call provided callback on unmount', () => {
+  const { unmount } = renderHook(() => useMount(mockCallback));
+  expect(mockCallback).toHaveBeenCalledTimes(1);
+
+  unmount();
+
+  expect(mockCallback).toHaveBeenCalledTimes(1);
+});
+
+it('should not call provided callback on rerender', () => {
+  const { rerender } = renderHook(() => useMount(mockCallback));
+  expect(mockCallback).toHaveBeenCalledTimes(1);
+
+  rerender();
+
+  expect(mockCallback).toHaveBeenCalledTimes(1);
+});

src/__tests__/useUnmount.test.ts

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+import { renderHook } from '@testing-library/react-hooks';
+import { useUnmount } from '..';
+
+const mockCallback = jest.fn();
+
+afterEach(() => {
+  jest.resetAllMocks();
+});
+
+it('should not call provided callback on mount', () => {
+  renderHook(() => useUnmount(mockCallback));
+
+  expect(mockCallback).not.toHaveBeenCalled();
+});
+
+it('should call provided callback on unmount', () => {
+  const { unmount } = renderHook(() => useUnmount(mockCallback));
+  expect(mockCallback).not.toHaveBeenCalled();
+
+  unmount();
+
+  expect(mockCallback).toHaveBeenCalledTimes(1);
+});
+
+it('should not call provided callback on rerender', () => {
+  const { rerender } = renderHook(() => useUnmount(mockCallback));
+  expect(mockCallback).not.toHaveBeenCalled();
+
+  rerender();
+
+  expect(mockCallback).not.toHaveBeenCalled();
+});