SDD

University of London CM 2010 Software Design and Development

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Topic 2 Test-Driven Development

Week 5 Test-Driven development

Reading

Basics

Three laws of unit-testing:

(PDF) Martin, R.C. ‘Professionalism and test-driven development’, IEEE Software 24(3) 2007, pp.32–36.

The following special issue on test-driven development contains several interesting articles:

IEEE Software 24(3) 2007.

Advanced readings and future trends

(PDF) Segura, S. and Z.Q. Zhou ‘Metamorphic testing 20 years later: a hands-on introduction’, 2018 IEEE/ACM 40th International Conference on Software Engineering: Companion (ICSE-Companion) 2018, pp.538–539.

(PDF) Borle, N., M. Feghhi, E. Stroulia, R. Grenier and A. Hindle ‘[Journal First] Analyzing the effects of test driven development in GitHub’, 2018 IEEE/ACM 40th International Conference on Software Engineering (ICSE) 2018, pp.1062–1062.

Learning Objectives

Define test-driven development
Identify the processes involved in test-driven development
Critically analyse examples of test-driven development in source code repositories

Three Laws of TDD

You may not write production code unless you’ve first written a failing unit test
You may not write more of a unit test than is sufficient to fail
You may not write more production code than is sufficient to make the failing unit test pass

Demo of unit test workflow

Requirement

R1: this function receives an array of integers and returns the highest

Test: does the getHighest function return a value?

Write a failed test.

function testReturnVal() {
    let input = [1, 2, 4, 5, 6];
    let result = getHighest(input);

    return !(result == undefined);
}

let result1 = testReturnVal();
if (result1) console.log("testReturnVal passed");
else console.log("testReturnVal failed");

// ReferenceError: getHighest is not defined

Write the minimum code to pass the test.

function getHighest(input) {
    return 0;
}

// testReturnVal passed

Test: does it return a value from the array?

function testResultInArray() {
let input = [1, 2, 3];
let result = getHighest(input);

return result == 1 || result == 2 || result == 3;
}

let result2 = testResultInArray();
if (result2) console.log("testResultInArray passed");
else console.log("testResultInArray failed");

// testReturnVal passed
// testResultInArray failed

Change getHighest() to:

function getHighest(input) {
    return input[0];
}

// testReturnVal passed
// testResultInArray passed

Test: does it return the correct array/value?

function testCorrectResult() {
    let input = [1, 2, 3];
    let result = getHighest(input);
    return result == 3;
}

...

let result3 = testCorrectResult();
if (result3) console.log("testCorrectResult passed");
else console.log("testCorrectResult failed");

// testReturnVal passed
// testResultInArray passed
// testCorrectResult failed

Change getHighest() to:

function getHighest(input) {

    let max = input[0];
    for (let i = 0; i < input.length; i++) {
        if (input[i] > max) max = input[i];
    }
    return max;
}

// testReturnVal passed
// testResultInArray passed
// testCorrectResult passed

Full test file in JavaScript

What to test?

interface testing: test if a function receives the correct input(s) and output(s), not user interface.
exercising data structure: verifying data structures’ been used correctly and being stored.
boundary testing: specifying boundaries in software.

i.e. a function takes an integer as input, what if I put in 0? what’s the highest value I can put in?

i.e. a function finds certain things in an array, can it find the first/last element correctly?
execution paths: tests deliberately go through all paths available in a given module.
error handling: is the error descriptive/intelligible? does the error match what actually happened? does itt reach the error handling code (i.e. crash before reach)?

Week 6 Unit testing in Python

Learning Objectives

Write unit tests using the Python unittest package
Describe the elements of a unit testing framework
Carry out the test-driven development workflow in Python

Reading

Python unittest

Unittest in Python

Python Script

import unittest

class TestSetForOneModule(unittest.TestCase):
    def test_arithmetic_pass(self):
        self.assertEqual(2+2, 4)

    def test_arithmetic_fail(self):
        self.assertEqual(2+2, 3)

unittest.main(argv=['ignored', '-v'], exit=False)

Week 7 Unit testing in C++

Learning Objectives

Write unit tests using the C++ cppunit package
Describe the elements of a unit testing framework
Carry out the test-driven development workflow in C++

Reading

cplusplus.com - Structure of a program

cppunit in C++

Week 8 Unit testing a web API

Learning Objectives

Write unit tests using the JavaScript Mocha package
Describe the elements of a unit testing framework
Carry out the test-driven development workflow

This week we will be working with various tools. You can use our browser-based JavaScript environment to carry out the work – in that case, you should not need to install anything.

If you plan to work on your own machine, you will be given instructions on which tools to install later, but you can get start now by installing Node.js. We recommend version 12 LTS.

We will be using Mocha and Chai to carry out the unit testing.

Might need Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass for PowerShell to run the tests.

Instructions