Day 3 code - asynchronous tests

doc/day3.md

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+# Day 3 notes - Asynchronous tests
+
+## Mocha `done`
+
+### Create new src file and test file
+
+* In your editor create a directory for source and test
+* Create src function and export it
+
+```javascript
+function day3() {
+}
+
+export default day3;
+```
+
+```javascript
+import {expect} from 'chai';
+import day3 from '../src/day3';
+
+describe('day 3 tests', () => {
+    it('', () => {
+    });
+});
+```
+
+* Run the tests
+
+```shell
+mocha --require babel-register
+```
+
+* Run only the day3 tests
+
+```shell
+mocha --require babel-register test/day3.test.js
+```
+
+## Add timeout test
+
+```javascript
+it('should return expected value from callback', () => {
+    day3((returnedData) => {
+        expect(returnedData).to.equal('hello');
+    });
+});
+```
+* Run the tests - they appear to pass
+* We've got no code yet!
+* Let's write the code
+
+```javascript
+function day3(callback) {
+    setTimeout(() => {
+        callback('hello');
+    }, 1000);
+}
+```
+
+* Run the tests - they still appear to pass
+* It thinks test is synchronous
+* Need to tell Mocha it's an asynchronous
+* Add done to callback function and call it when we've done
+
+```javascript
+it('should return expected value from callback', (done) => {
+    day3((returnedData) => {
+        expect(returnedData).to.equal('hello');
+        done();
+    });
+});
+```
+
+## Promises
+
+```javascript
+it('should return expected value from promise', () => {
+    day3()
+        .then((returnedData) => {
+            expect(returnedData).to.equal('hello');
+        });
+});
+```
+
+```javascript
+function day3(callback) {
+    if (callback) {
+        setTimeout(() => {
+            callback('hello');
+        }, 1000);
+    } else {
+        return Promise.resolve('hello');
+    }
+}
+```
+
+* Test to return a promise which does the same
+* Gotcha : Not using done - tests pass
+* Use `done` again
+
+```javascript
+it('should return expected value from promise', (done) => {
+    day3()
+        .then((returnedData) => {
+            expect(returnedData).to.equal('hello');
+            done();
+        });
+});
+```
+
+* Better way - return a promise
+
+```javascript
+it('should return expected value from promise', () => {
+    return day3()
+        .then((returnedData) => {
+            expect(returnedData).to.equal('hello');
+        });
+});
+```

src/day3.js

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+function day3(callback) {
+    if (callback) {
+        setTimeout(() => callback('hello'), 1000);
+    } else {
+        return Promise.resolve('hello');
+    }
+}
+
+
+export default day3;

test/day3.test.js

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+import {expect} from 'chai';
+import day3 from '../src/day3';
+
+describe('day 3 tests', () => {
+    it('should return expected value from callback', (done) => {
+        day3((returnedData) => {
+            expect(returnedData).to.equal('hello');
+            done();
+        });
+    });
+
+    it('should return expected value from promise with done', (done) => {
+        day3()
+            .then((returnedData) => {
+                expect(returnedData).to.equal('hello');
+                done();
+            });
+    });
+
+    it('should return expected value from promise', () => {
+        return day3()
+            .then((returnedData) => {
+                expect(returnedData).to.equal('hello');
+            });
+    });
+});