源代码：describe函数传入的两个参数：描述信息和箭头函数：

从注释能看出，describe函数的语义：Create a group of specs (often called a suite)

getJasmineRequireObj().interface = function(jasmine, env) {var jasmineInterface = {/*** Callback passed to parts of the Jasmine base interface.** By default Jasmine assumes this function completes synchronously.* If you have code that you need to test asynchronously, you can declare that you receive a `done` callback, return a Promise, or use the `async` keyword if it is supported in your environment.* @callback implementationCallback* @param {Function} [done] Used to specify to Jasmine that this callback is asynchronous and Jasmine should wait until it has been called before moving on.* @returns {} Optionally return a Promise instead of using `done` to cause Jasmine to wait for completion.*//*** Create a group of specs (often called a suite).** Calls to `describe` can be nested within other calls to compose your suite as a tree.* @name describe* @since 1.3.0* @function* @global* @param {String} description Textual description of the group* @param {Function} specDefinitions Function for Jasmine to invoke that will define inner suites and specs*/describe: function(description, specDefinitions) {return env.describe(description, specDefinitions);},

参数定义

• description：Textual description of the group
• specDefinitions: Function for Jasmine to invoke that will define inner suites and specs

从这里能看出，单元测试代码运行于一个特定的zone里：

 // Monkey patch all of the jasmine DSL so that each function runs in appropriate zone.var jasmineEnv = jasmine.getEnv();['describe', 'xdescribe', 'fdescribe'].forEach(function (methodName) {var originalJasmineFn = jasmineEnv[methodName];jasmineEnv[methodName] = function (description, specDefinitions) {return originalJasmineFn.call(this, description, wrapDescribeInZone(specDefinitions));};});

addSpecsToSuite：

添加Specs到Suite之后，执行：

 /*** Gets a function wrapping the body of a Jasmine `describe` block to execute in a* synchronous-only zone.*/function wrapDescribeInZone(describeBody) {return function () {return syncZone.run(describeBody, this, arguments);};}

在一个同步zone里执行spec的body，即传入describe方法的箭头函数：

callback就是应用程序单元测试代码里定义的箭头函数：

即如下图所示：

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