Warn about spying on the console

Author: bvaughn

scripts/jest/setupTests.js

@@ -13,8 +13,21 @@ if (process.env.REACT_CLASS_EQUIVALENCE_TEST) {
   // https://github.com/facebook/jest/blob/v20.0.4/packages/jest-matchers/src/spyMatchers.js#L160
   const isSpy = spy => spy.calls && typeof spy.calls.count === 'function';
 
-  const spyOn = global.spyOn;
+  // This is the Jasmine spyOn() method.
+  // Unlike jest.spyOn(), it does not pass through to the method it spies on by default.
+  const jasmineSpyOn = global.spyOn;
+
   const noop = function() {};
+  const spyOn = function(object, methodName) {
+    if (object === console) {
+      throw new Error(
+        'Do not spy on the console directly. ' +
+          'Use toWarnDev() or toLowPriorityWarnDev() instead.'
+      );
+    }
+
+    jasmineSpyOn(object, methodName);
+  };
 
   // Spying on console methods in production builds can mask errors.
   // This is why we added an explicit spyOnDev() helper.