fix(timers): safe check for setImmediate and clearImmediate (#916)

Co-authored-by: Kent C. Dodds <me+github@kentcdodds.com>

src/__tests__/helpers.js

@@ -97,4 +97,23 @@ describe('run with real timers', () => {
     })
     expect(global.setTimeout).toBe(fakedSetTimeout)
   })
+
+  describe('run with setImmediate and clearImmediate deleted', () => {
+    const setImmediate = global.setImmediate
+    const clearImmediate = global.clearImmediate
+
+    beforeEach(() => {
+      delete global.setImmediate
+      delete global.clearImmediate
+    })
+
+    afterEach(() => {
+      global.setImmediate = setImmediate
+      global.clearImmediate = clearImmediate
+    })
+
+    test('safe check for setImmediate and clearImmediate', () => {
+      expect(() => runWithRealTimers(() => {})).not.toThrow()
+    })
+  })
 })

src/helpers.js

@@ -16,14 +16,21 @@ function runWithRealTimers(callback) {
 
 function runWithJestRealTimers(callback) {
   const timerAPI = {
-    clearImmediate,
     clearInterval,
     clearTimeout,
-    setImmediate,
     setInterval,
     setTimeout,
   }
 
+  // For more on why we have the check here,
+  // checkout https://github.com/testing-library/dom-testing-library/issues/914
+  if (typeof setImmediate === 'function') {
+    timerAPI.setImmediate = setImmediate
+  }
+  if (typeof clearImmediate === 'function') {
+    timerAPI.clearImmediate = clearImmediate
+  }
+
   jest.useRealTimers()
 
   const callbackReturnValue = callback()