chapter 04: copy code from chapter 03 to the chapter 04 folder in order to continue with the book

Author: devcorpio

chapter_04-interaction-testing-using-mock-objects/LogAn/ArgumentError.js

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+class ArgumentError extends Error {}
+
+module.exports = ArgumentError;

chapter_04-interaction-testing-using-mock-objects/LogAn/alwaysValidFakeExtensionManager.js

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+function alwaysValidFakeExtensionManager() {
+    /**
+     * @param {string} fileName
+     * @return {Promise}
+     */
+    async function isValid(fileName) {
+        return true;
+    }
+
+    return {
+        isValid,
+    };
+}
+
+module.exports = alwaysValidFakeExtensionManager;

chapter_04-interaction-testing-using-mock-objects/LogAn/extensionManager.js

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+const fileExtensionManagerFactory = require('./fileExtensionManager');
+
+function extensionManager() {
+    let customManager = null;
+
+    function create() {
+        if (customManager !== null) {
+            return customManager;
+        }
+
+        return fileExtensionManagerFactory();
+    }
+
+    function setManager(manager) {
+        customManager = manager;
+    }
+
+    return {
+        create,
+        setManager,
+    };
+}
+
+module.exports = extensionManager;

chapter_04-interaction-testing-using-mock-objects/LogAn/fakeExtensionManager.js

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+function fakeExtensionManager() {
+    /**
+     * @type {boolean}
+     */
+    let valid = false;
+
+    /**
+     * @param {boolean} value
+     */
+    function willBeValid(value) {
+        valid = value;
+    }
+
+    /**
+     * @param {string} fileName
+     */
+    async function isValid(fileName) {
+        return valid;
+    }
+
+    return {
+        willBeValid,
+        isValid,
+    };
+}
+module.exports = fakeExtensionManager;

chapter_04-interaction-testing-using-mock-objects/LogAn/fileExtensionManager.js

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+const fs = require('fs');
+const util = require('util');
+
+const readFilePromisied = util.promisify(fs.readFile);
+
+function fileExtensionManager() {
+    /**
+     * @param {string} fileName
+     * @return {Promise}
+     */
+    async function isValid(fileName) {
+        const fileNameExtensions = await readFilePromisied(
+            `${__dirname}/fileNameExtensions.config.json`,
+            'utf8'
+        ).then(fileContent => JSON.parse(fileContent).extensions);
+
+        const isValidExtension = fileNameExtensions.some(
+            function checkFileNameExtension(extension) {
+                if (
+                    fileName
+                        .toUpperCase()
+                        .endsWith(`.${extension.toUpperCase()}`)
+                ) {
+                    return true;
+                }
+
+                return false;
+            }
+        );
+
+        return isValidExtension;
+    }
+
+    return {
+        isValid,
+    };
+}
+
+module.exports = fileExtensionManager;

chapter_04-interaction-testing-using-mock-objects/LogAn/fileNameExtensions.config.json

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+{
+    "extensions": ["slf", "sql"]
+}

chapter_04-interaction-testing-using-mock-objects/LogAn/logAnalyzer.class.js

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+const ArgumentError = require('./ArgumentError');
+const fileExtensionManagerFactory = require('./fileExtensionManager');
+
+class LogAnalyzer {
+    constructor() {
+        /**
+         * @type {boolean}
+         */
+        this.wasLastFileNameValid = false;
+    }
+    /**
+     * @return {boolean}
+     */
+    getWasLastFileNameValid() {
+        return this.wasLastFileNameValid;
+    }
+
+    /**
+     * a virtual function created to use "Extract and Override" technique
+     */
+    getManager() {
+        return fileExtensionManagerFactory();
+    }
+
+    /**
+     * @param {string} fileName
+     * @return {Promise}
+     */
+    async isValidLogFileName(fileName) {
+        this.wasLastFileNameValid = false;
+
+        if (fileName === '') {
+            throw new ArgumentError('filename has to be provided');
+        }
+
+        const result = await this.getManager().isValid(fileName);
+
+        if (!result) {
+            return false;
+        }
+
+        this.wasLastFileNameValid = true;
+        return true;
+    }
+}
+
+module.exports = LogAnalyzer;

chapter_04-interaction-testing-using-mock-objects/LogAn/logAnalyzer.js

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+const ArgumentError = require('./ArgumentError');
+
+function logAnalyzer(extensionManager) {
+    /**
+     * @type {boolean}
+     */
+    let wasLastFileNameValid;
+
+    /**
+     * @return {boolean}
+     */
+    function getWasLastFileNameValid() {
+        return wasLastFileNameValid;
+    }
+
+    /**
+     * @param {string} fileName
+     * @return {Promise}
+     */
+    async function isValidLogFileName(fileName) {
+        wasLastFileNameValid = false;
+
+        if (fileName === '') {
+            throw new ArgumentError('filename has to be provided');
+        }
+
+        const result = await extensionManager.isValid(fileName);
+
+        if (!result) {
+            return false;
+        }
+
+        wasLastFileNameValid = true;
+        return true;
+    }
+
+    return {
+        getWasLastFileNameValid,
+        isValidLogFileName,
+    };
+}
+
+module.exports = logAnalyzer;

chapter_04-interaction-testing-using-mock-objects/LogAn/logAnalyzer.test.js

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+const logAnalyzerFactory = require('./logAnalyzer');
+const fakeExtensionManagerFactory = require('./fakeExtensionManager');
+const extensionManagerFactory = require('./extensionManager');
+
+// imported to try the technique "Extract and override"
+const TestableLogAnalyzerClass = require('./testableLogAnalyzer.class');
+
+let myFakeExtensionManager;
+
+beforeEach(() => {
+    myFakeExtensionManager = fakeExtensionManagerFactory();
+});
+
+describe.each([
+    ['johndoe.js', false],
+    ['johndoe.slf', true],
+    ['johndoe.SLF', true],
+])('isValidLogFileName("%s"))', (fileName, expected) => {
+    it(`bad extension returns ${expected}`, async () => {
+        myFakeExtensionManager.willBeValid(expected);
+
+        const logAnalyzer = logAnalyzerFactory(myFakeExtensionManager);
+        const result = await logAnalyzer.isValidLogFileName(fileName);
+        expect(result).toBe(expected);
+    });
+});
+
+describe('isValidLogFileName', () => {
+    it('empty filename throws error', async () => {
+        async function emptyLogFileName() {
+            const logAnalyzer = logAnalyzerFactory(myFakeExtensionManager);
+
+            return logAnalyzer.isValidLogFileName('');
+        }
+
+        await expect(emptyLogFileName()).rejects.toThrow(
+            'filename has to be provided'
+        );
+    });
+
+    /**
+     * an example of state-based testing
+     */
+    it.each`
+        fileName         | expected
+        ${'johndoe.foo'} | ${false}
+        ${'johndoe.slf'} | ${true}
+    `(
+        'when called there changes wasLastFileNameValid that returns $expected',
+        async ({ fileName, expected }) => {
+            myFakeExtensionManager.willBeValid(expected);
+
+            const logAnalyzer = logAnalyzerFactory(myFakeExtensionManager);
+            await logAnalyzer.isValidLogFileName(fileName);
+            const result = logAnalyzer.getWasLastFileNameValid();
+
+            expect(result).toBe(expected);
+        }
+    );
+
+    /**
+     * an example of use of "injecting a fake just before a method call"
+     * right now I'm not injecting a fake, and extensionManager is returning fileExtensionManager,
+     * therefore this test is an integration test and not a unit test!!!!
+     */
+    it('return true using extensionManagerFactory', async () => {
+        const extensionManager = extensionManagerFactory();
+        const logAnalyzer = logAnalyzerFactory(extensionManager.create());
+        const result = await logAnalyzer.isValidLogFileName('johndoe.sql');
+
+        expect(result).toBe(true);
+    });
+
+    /**
+     * an example of use of "injecting a fake just before a method call"
+     * In this case I'm setting a fake extension manager, that converts this in a unit test!!, because
+     * right now I have not external dependencies.
+     */
+    it('return true using extensionManagerFactory', async () => {
+        myFakeExtensionManager.willBeValid(true);
+        const extensionManager = extensionManagerFactory();
+        extensionManager.setManager(myFakeExtensionManager);
+
+        const logAnalyzer = logAnalyzerFactory(extensionManager.create());
+        const result = await logAnalyzer.isValidLogFileName('johndoe.sql');
+
+        expect(result).toBe(true);
+    });
+
+    /**
+     * I'm using the tecnique "Extract and override", this technique has several steps:
+     *
+     * step 1: create a virtual function in the unit under test(logAnalyzer.js in this case)
+     *    that returns the real extension manager, the one that works with the filesystem
+     *
+     * step 2: create a class that extends of it
+     *
+     * step3: use this new class to create the tests!! :)
+     */
+    it('return false using testableLogAnalyzer', async () => {
+        const expected = false;
+        myFakeExtensionManager.willBeValid(expected);
+
+        const logAnalyzer = new TestableLogAnalyzerClass(
+            myFakeExtensionManager
+        );
+        const result = await logAnalyzer.isValidLogFileName('johndoe.ts');
+
+        expect(result).toBe(expected);
+    });
+});

chapter_04-interaction-testing-using-mock-objects/LogAn/testableLogAnalyzer.class.js

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+const fakeExtensionManagerFactory = require('./fakeExtensionManager');
+const logAnalizer = require('./logAnalyzer.class');
+
+class TestableLogAnalyzer extends logAnalizer {
+    constructor(extensionManager) {
+        super();
+        this.manager = extensionManager;
+    }
+    getManager() {
+        return this.manager;
+    }
+}
+
+module.exports = TestableLogAnalyzer;