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November 10, 2016 16:58
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This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -0,0 +1,95 @@ // 75: Promise - basics // To do: make all tests pass, leave the assert lines unchanged! describe('a Promise represents an operation that hasn`t completed yet, but is expected in the future', function() { it('`Promise` is a global function', function() { const expectedType = 'function'; assert.equal(typeof Promise, expectedType); }); describe('the constructor', function() { it('instantiating it without params throws', function() { const fn = () => { Promise() } assert.throws(fn); }); it('expects a function as parameter', function() { const param = () => {}; assert.doesNotThrow(() => { new Promise(param); }); }); }); describe('simplest promises', function() { it('resolve a promise by calling the `resolve` function given as first parameter', function(done) { let promise = new Promise((resolve) => { resolve(); }); promise .then(() => done()) .catch(() => done(new Error('The promise is expected to resolve.'))); }); it('the `resolve` function can return a value, that is consumed by the `promise.then()` callback', function(done) { let promise = new Promise((resolve) => { resolve(42); }); promise .then(value => {assert.equal(value, 42); done(); }) .catch(() => done(new Error('The promise is expected to resolve with 42!'))); }); it('rejecting a promise is done by calling the callback given as 2nd parameter', function(done) { let promise = new Promise((resolve, reject) => { reject(); }); promise .then(() => done(new Error('The promise is expected to be rejected.'))) .catch(() => done()); }); }); describe('an asynchronous promise', function() { it('can resolve later, also by calling the first callback', function(done) { let promise = new Promise((resolve) => { setTimeout(() => resolve(), 100); }); promise .then(() => done()) .catch(() => done(new Error('The promise is expected to resolve.'))); }); it('reject it at some later point in time, calling the 2nd callback', function(done) { let promise = new Promise((resolve, reject) => { setTimeout(() => reject(), 100); }); promise .then(() => done(new Error('The promise is expected to be rejected.'))) .catch(() => done()); }); }); describe('test library (mocha here) support for promises', function() { it('just returning the promise makes the test library check that the promise resolves', function() { let promise = new Promise((resolve, reject) => { resolve() }); // return the promise to mocha, it has the checking for promise resolving built in, when it receives a promise return promise; }); }); });