Test driven development

TEST DRIVEN DEVELOPMENT
John Walsh

Outline
2

Outline

1. Development Approaches
2. What is TDD
3. Code Refactoring
4. Steps to start TDD
5. What can be tested
6. How Does TDD Help
7. Unit Tests
8. Unit Test – Definitions
9. Code Coverage
10. Example
11. Visual Studio Unit Tests Walkthrough

Development Approaches
3

 Ad hoc development
 Writing pseudo code first
 Model Driven Development (MDD)
 Test Driven Development (TDD)

What is TDD
4

Test-Driven Development (TDD) is a software development technique that involves (repeatedly)
first writing a test case and then implementing the code necessary to excercise the test

(Test case First, Then Code)

In TDD:

Requirements => Tests => developement Code
 Requirements drive the tests.

 Tests drive the development of the application code.

 No application code is written without writing a failing test first.

 Tests are collected in a suite and the suite is run frequently, like every time after code is written.

 Test and code are written in elementary increments.

 Refactoring is a continuous operation, and is supported by a passing battery of tests.

What is TDD
5

1. The developer writes an (initially failing) automated test
case
2. that defines a desired requirement (improvement or
new function) .
3. He then produces the minimum amount of code to pass
that test
4. and finally refactors the new code to acceptable
standards

What is TDD
6

Test should
TDD = Test First Development + Refactoring Initially Fail
(and for
expected
•Add a Test + ensure it fails reason)

•Write minimum amount of code to get it to pass

•Refractor code , all the while re-running tests to
ensure they pass

Code Refactoring
7

 Refactoring is a disciplined technique for restructuring an existing
body of code, altering its internal structure without changing its
external behaviour.
 Code Improvement
 Refactoring Removes „code smell‟
 long methods,
 duplicate code,
 large classes
 Refactoring techniques
 Breaking large methods up into smaller, reusable, more logical units
 By breaking down code in smaller pieces, it is more easily understandable => less
buggy + should be
 Move part of code to new class
 create more general types to allow for more code sharing

Steps to start TDD
8

1) Analyze the requirements + write the list of tasks or
features
2) Pick a task or feature
 Brainstorm a list of tests for the task or feature
 Review the tests list and pick a test
3) Write the test case
1) Write only enough code that the test case compiles
4) Run the test and see running the code fails
5) Write only enough code to just pass the test
6) Refactor the production code and eliminate duplication
7) Repeat

What can be tested
9

 Valid inputs
 Invalid inputs
 Errors, exceptions, and events
 Boundary conditions
 Everything that could possibly break!

How Does TDD Help
10

 Ensures that your design is clean by focusing on creation of operations that are callable
and testable

 Shortens the programming feedback loop

 Provides detailed specification through tests

 Provides concrete evidence that your software works

 The suite of unit tests provides constant feedback that each component is still working.

 Supports evolutionary development.

 The unit tests act as documentation that cannot go out-of-date, unlike separate
documentation, which can and frequently does.

 The software tends to be better designed, that is, loosely coupled and easily maintainable,
because the developer is free to make design decisions and refactor at any time with
confidence that the software is still working. This confidence is gained by running the tests.
The need for a design pattern may emerge, and the code can be changed at that time.

TDD Advantages
11

TDD is good because it:
 Aids in understanding (and even defining) requirements
 It‟s a practice that adds reliability to the development process
 Tests Improve Design
 Testing Makes Development Faster, because less time is spent chasing bugs.
 catch defects early in the development cycle (earlier is better)

 Improves code quality because of the increased modularity, and continuous and relentless refactoring.
 Decreases maintenance costs because the code is easier to follow.
 Testing is “automated”
 If the test fails, it's obvious where to look for the problem (if test written correctly i.e test one thing)
 Reduces the number of bugs by orders of magnitude,
 QA will receive functioning code (they can focus more on end to end and integration)
 TDD promotes “small steps”, and lots of them
 TDD is risk averse programming, investing work in the near term to avoid failures later on” Munjal
Budhabhatti, The Architecture Journal 14

Unit Tests
12

General Definition:

A method of testing the correctness of a particular module of
source code -Wikipedia

Testing a method in a class you are writing – while you are
writing that class. Chris Donnan

Unit Test - Definitions
13

 Test Fixture/ Test Class – A class with some unit tests in it.

 Test (or Test Method) – a test implemented in a Test Class

 Test Suite - A set of test grouped together

 Test Harness/ Runner – The tool that actually executes the
tests.

Code Coverage
14

 Code Coverage is an approach or technique that sees you executing [all]
the statements and paths through your code-base
 Which code has been touched by a test.

 Identifies code that your tests missed
 Thus, you should find bugs you may not otherwise have found, code
coverage “gives you clues”
 Identifies code that does not have a test case exercising it

 Code coverage can be a useful metric, but it must be used with care
 Determine whether high code coverage is a good thing
 Simply “touching” every line of code might not be suitable

 Do not be sucked into “writing quick tests” just to improve coverage

The tools
15
 NUnit 2.4.6
 Testing framework for .NET
 Graphical front-end (clear “black/white” pass/fail indicator)

 NCover 1.5.8
 “Do you know how much of your code is being tested”
 Command-line
 Creates an XML output file, XSL transformation for viewing

 NCoverExplorer 1.4.0.7
 Graphical front-end for NCover
 Windows application that uses NCover‟s XML output file

 TestDriven.NET 2.11.2177
 NUnit, NCover, NCoverage integration inside the Visual Studio IDE
 Right-click context-sensitive menu
 Free “liberal” personal edition; commercial Profession and Enterprise editions

Example
16

 We want to develop a method that,
 given two Integers,
 returns an Integer that is the sum of parameters.

Example (cont.)
17

 Test  Method

Integer i = new
Integer(5);
Integer j = new
Integer(2);

Object o = sum(i,j);

Example (cont.)
18

 Test  Method

Integer i = new
public static Object
Integer(5);
sum(Integer i,
Integer j = new
Integer(2); Integer j)
{
Object o = sum(i,j); return new
Object();
}

Example (cont.)
19

 Test  Method

Integer i = new
public static Object
Integer(5);
sum(Integer i,
Integer j = new
{
if (o instanceof Integer) Object();
return true; }
else
return false;

Example (cont.)
20

 Test  Method

Integer i = new
public static Integer
Integer(5);
sum(Integer i,
Integer j = new
{
if (o instanceof Integer) Integer();
return true; }
else
return false;

Example (cont.)
21

 Test  Method
Integer i = new
Integer(5); public static Integer
Integer j = new sum(Integer i,
{
if (o instanceof Integer) return new
Integer();
&& ((new
Integer(7)).equals(o)) }
return true;
else
return false;

Example (cont.)
22

 Test  Method
Integer i = new
Integer(5); public static Integer
Integer j = new sum(Integer i,
{
if (o instanceof Integer) return new
Integer(
&& ((new
Integer(7)).equals(o)) i.intValue() +
j.intValue());
return true;
else
);
return false; }

Visual Studio Unit Test WalkThrough
Unit Test Overview
24

 You can create unit tests by
1. using a code generation feature that creates the initial source code of the test,
2. or you can write the test completely by hand.
Either way, the test class and all test methods are identified by using programmatic
attributes.
 Programmatic Attributes (assigned automatically using „Code Generation‟)
• Each test class is marked with the [TestClass()] attribute
• Each unit test is a test method that is marked with the [TestMethod()] attribute.

 The Unit Testing Framework provides many additional Assert classes and other classes
that give you flexibility in writing unit test.
 The Microsoft.VisualStudio.TestTools.UnitTesting namespace supplies classes that provide unit
testing support.

 Using unit tests, you can test not only public methods but private methods as well.

Creating Unit Tests – Auto Generate
25

Select method in class you want to generate test for → Right-
click on method name → Select „Create Unit Tests‟

Creating Unit Tests – Auto Generate
26

 Method will be „checked‟ in pop-up box (you can select other
methods, I‟ve also selected Credit method!) and click OK.
 You can click on settings to update some general setting for Test (I‟ve
changed the Test file name to be more descriptive

Creating Unit Tests – Auto Generate Each test class is
marked with the
27 [TestClass()] attribute

1.A separate unit test is created for
each method that you select in the Each unit test is a test
Create Unit Test dialog box. (here method that is marked
we have unit tests for the Credit with the [TestMethod()]
and Debit methods. attribute

2.Each unit tests that is generated
has empty variables and a
placeholder Assert statement (the
default is usually the
Assert.Inconclusive statement.

• To make the test meaningful,
you have to initialize the
variables and replace the
placeholder with an
appropriate Assert statement.

3.When you first generate unit tests,
a test project is created in your
solution.

4.For each class you are testing, a
separate unit test file is created. In
this example, both of the methods
we are testing belong to the same
class. Therefore, there is only one
unit test file, BankAccountTest.cs.

Visual Studio Unit Tests
Creating Unit Tests – Manually
28
To manually create a test, right click on Test project -> Add ->
New Test

Updating A Unit Test
29

Update Test Method to test desired functionality

Edit Generated Code To

Running Unit Tests
30
View and select test to run

View Results of test run

Organise Tests into Groups/Lists

Configure Code Coverage
31

 To see what proportion of your project's code is actually being tested, use the
code coverage feature of Microsoft Visual Studio 2010.

Double click on
“Local.Testing” in the
solution explorer, and
select “Data And
diagnostics”

1.Select „Code
coverage‟
2.Configure Items to
include
3.Click Ok and then
„Save as‟ and
replace existing
„local.testing‟ file

32

 Ensure „Active Test
Settings‟ is set to
„local.testsettings‟

 Run Tests in „Test List
Editor‟

 View Coverage Info in
„Code coverage Results‟
Window (viewable from
Test-→ Windows →Code
Coverage Results)

33

 Code Coverage Results Window

Appendix – Assert Methods
34

 Unit Test Framework => Microsoft.VisualStudio.TestTools.UnitTesting
 Assert Methods

 Inconclusive() : Indicates that the assertion cannot be verified.

 Inconclusive(String) : Indicates that the assertion cannot be verified & display a message

 AreEqual(Object, Object)

 AreNotEqual(Object, Object)

 AreNotSame(Object, Object) :Ref comparison

 IsTrue(Boolean)

 IsFalse(Boolean)

 IsNull(Object)

 IsNotNull(Object)

Appendix – Test Attributes
35

 Unit Test Framework => Attributes
 [TestClass()] : identify class that contains Test method

 [TestMethod()] : identify Test method

 [TestInitialize()] : identifies method that will be run before each test

 [TestCleanup()] : identifies method that will be run after each test

 [ExpectedException(exceptionType)] : Indicates that an exception is expected during test
method execution. (The test method will pass if the expected exception is thrown.)

See “Microsoft.VisualStudio.TestTools.UnitTesting Namespace” for list of attributes
http://msdn.microsoft.com/en-us/library/microsoft.visualstudio.testtools.unittesting(v=vs.100).aspx

References
36

 Microsoft (VS 2010): Walkthrough: Creating and Running Unit Tests
 http://msdn.microsoft.com/en-us/library/ms182532(v=vs.100).aspx

 Microsoft (VS 2010) : Walkthrough: Run Tests and View Code Coverage

 Microsoft (VS 2008) : Walkthrough: Working with Unit Tests

 Microsoft (VS 2008) : Guidelines for Test-Driven Development
 http://msdn.microsoft.com/en-US/library/aa730844(v=VS.80).aspx

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