Fail jest tests on any un-spied warnings

Originally #4223 -- we lost this when we switched to jest.

scripts/jest/test-framework-setup.js

@@ -0,0 +1,35 @@
+'use strict';
+
+var env = jasmine.getEnv();
+
+var oldError = console.error;
+var newError = function() {
+  oldError.apply(this, arguments);
+  var spec = env.currentSpec;
+  if (spec) {
+    var expectationResult = new jasmine.ExpectationResult({
+      passed: false,
+      message:
+        'Expected test not to warn. If the warning is expected, mock it ' +
+        'out using spyOn(console, \'error\'); and test that the warning ' +
+        'occurs.',
+    });
+    spec.addMatcherResult(expectationResult);
+  }
+};
+console.error = newError;
+
+// Make sure console.error is set back at the end of each test, or else the
+// above logic won't work
+afterEach(function() {
+  // TODO: Catch test cases that call spyOn() but don't inspect the mock
+  // properly.
+
+  if (console.error !== newError && !console.error.isSpy) {
+    var expectationResult = new jasmine.ExpectationResult({
+      passed: false,
+      message: 'Test did not tear down console.error mock properly.',
+    });
+    env.currentSpec.addMatcherResult(expectationResult);
+  }
+});