fix: safe check for setImmediate and clearImmediate

Jest is planning to sandbox setImmediate, and this would not work since
setImmediate and clearImmediate would
be undefined.

Author: renatoalencar

src/helpers.js

@@ -16,14 +16,19 @@ function runWithRealTimers(callback) {
 
 function runWithJestRealTimers(callback) {
   const timerAPI = {
-    clearImmediate,
     clearInterval,
     clearTimeout,
-    setImmediate,
     setInterval,
     setTimeout,
   }
 
+  if (typeof setImmediate === 'function') {
+    timerAPI.setImmediate = setImmediate
+  }
+  if (typeof clearImmediate === 'function') {
+    timerAPI.clearImmediate = clearImmediate
+  }
+
   jest.useRealTimers()
 
   const callbackReturnValue = callback()