Allow generator functions to be passed to .and.callFake

Fixes #1848.

spec/core/SpyStrategySpec.js

@@ -334,6 +334,17 @@ describe('SpyStrategy', function() {
     }).toThrowError(/^Argument passed to callFake should be a function, got/);
   });
 
+  it('allows generator functions to be passed to callFake strategy', function() {
+    jasmine.getEnv().requireGeneratorFunctions();
+
+    var generator = jasmine.getEnv().makeGeneratorFunction('yield "ok";'),
+      spyStrategy = new jasmineUnderTest.SpyStrategy({ fn: function() {} });
+
+    spyStrategy.callFake(generator);
+
+    expect(spyStrategy.exec().next().value).toEqual('ok');
+  });
+
   it('allows a return to plan stubbing after another strategy', function() {
     var originalFn = jasmine.createSpy('original'),
       fakeFn = jasmine.createSpy('fake').and.returnValue(67),

spec/helpers/generator.js

@@ -0,0 +1,22 @@
+(function(env) {
+  function getGeneratorFuncCtor() {
+    try {
+      eval('var func = function*() {}');
+    } catch (e) {
+      return null;
+    }
+
+    return Object.getPrototypeOf(func).constructor;
+  }
+
+  env.makeGeneratorFunction = function(text) {
+    var GeneratorFunction = getGeneratorFuncCtor();
+    return new GeneratorFunction(text || '');
+  };
+
+  env.requireGeneratorFunctions = function() {
+    if (!getGeneratorFuncCtor()) {
+      env.pending('Environment does not support generator functions');
+    }
+  };
+})(jasmine.getEnv());

spec/support/jasmine-browser.js

@@ -18,6 +18,7 @@ module.exports = {
   specFiles: ['**/*[Ss]pec.js', '!npmPackage/**/*'],
   helpers: [
     'helpers/asyncAwait.js',
+    'helpers/generator.js',
     'helpers/BrowserFlags.js',
     'helpers/checkForMap.js',
     'helpers/checkForSet.js',

spec/support/jasmine.json

@@ -6,6 +6,7 @@
   ],
   "helpers": [
     "helpers/asyncAwait.js",
+    "helpers/generator.js",
     "helpers/checkForMap.js",
     "helpers/checkForSet.js",
     "helpers/checkForSymbol.js",