test: using fake timers globally

packages/lib/src/spatial-navigation/components/virtualizedGrid/SpatialNavigationVirtualizedGrid.test.tsx

@@ -48,7 +48,6 @@ describe('SpatialNavigationVirtualizedGrid', () => {
     );
 
   it('renders the correct number of item', () => {
-    jest.useFakeTimers();
     const component = renderGrid();
     act(() => jest.runAllTimers());
 
@@ -74,7 +73,6 @@ describe('SpatialNavigationVirtualizedGrid', () => {
   });
 
   it('renders the correct number of item', () => {
-    jest.useFakeTimers();
     const component = renderGrid();
     act(() => jest.runAllTimers());
 

packages/lib/src/spatial-navigation/components/virtualizedList/SpatialNavigationVirtualizedList.test.tsx

@@ -48,7 +48,6 @@ describe('SpatialNavigationVirtualizedList', () => {
     );
 
   it('renders the correct number of item', () => {
-    jest.useFakeTimers();
     const component = renderList();
     act(() => jest.runAllTimers());
 
@@ -75,7 +74,6 @@ describe('SpatialNavigationVirtualizedList', () => {
   });
 
   it('handles correctly RIGHT and RENDERS new elements accordingly while deleting elements that are too far from scroll', async () => {
-    jest.useFakeTimers();
     const component = renderList();
     act(() => jest.runAllTimers());
 

packages/lib/src/testing/constants.ts

@@ -0,0 +1,11 @@
+/**
+ * UTC+1 in Winter (the default date is in Winter)
+ */
+export const TEST_DEFAULT_TZ = 'Europe/Paris';
+
+/**
+ * 15:23 UTC -> 16:23 In Paris
+ */
+export const TEST_DEFAULT_DATE = '2023-03-05T15:23:49.294Z';
+
+export const TEST_DEFAULT_MATH_RANDOM = 0.372294134538401;

packages/lib/src/testing/jest-setupAfterEnv.ts

@@ -1,3 +1,38 @@
 import '@testing-library/jest-native/extend-expect';
 
-export {};
+import { TEST_DEFAULT_DATE, TEST_DEFAULT_MATH_RANDOM } from './constants';
+
+/**
+ * Some globals have no reason to not ever be mocked if we want to have reproducible tests.
+ * Put those things here: Date, Math.random, etc.
+ *
+ * You can still customize the mock in an isolated way for a given test or test suite
+ * BEWARE that your customizations in tests and test suites don't apply to top-level module code (it runs before the `beforeEach`)
+ */
+const setupPermanentMocks = () => {
+  // Note: Timezone is set in src/testing/jest-globalSetup.ts (it wouldn't work to set it here)
+  jest.useFakeTimers({
+    // We're not really interested in stopping the microtasks queue, what we want to mock is "timers"
+    doNotFake: [
+      'setImmediate', // see https://github.com/callstack/react-native-testing-library/issues/1347
+      'clearImmediate',
+      'nextTick',
+      'queueMicrotask',
+      'requestIdleCallback',
+      'cancelIdleCallback',
+      'requestAnimationFrame',
+      'cancelAnimationFrame',
+      'hrtime',
+      'performance',
+    ],
+    now: new Date(TEST_DEFAULT_DATE), // To customize in a test, use `jest.setSystemTime`
+  });
+
+  Math.random = () => TEST_DEFAULT_MATH_RANDOM; // To customize in a given test, use `jest.spyOn(Math, "random").mockReturnValue(xx)`
+};
+
+// Some code runs before `beforeEach` (top-level code from imported modules), so this line is needed
+setupPermanentMocks();
+
+// And then this one is needed to re-set the mocks after the automatic `clearMocks`
+beforeEach(setupPermanentMocks);