Test driven development

TEST DRIVEN DEVELOPMENTJohn Walsh

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Outline

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

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Development Approaches

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

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What is TDD

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.

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What is TDD

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

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What is TDD

TDD = Test First Development + Refactoring

• Add a Test + ensure it fails

• Write minimum amount of code to get it to pass

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

Test should Initially Fail (and for expected reason)

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Code Refactoring

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

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Steps to start TDD

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

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What can be tested

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

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How Does TDD Help

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.

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TDD Advantages

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

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Unit Tests

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

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Unit Test - Definitions

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.

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Code Coverage

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

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The tools

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

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Example

We want to develop a method that,

given two Integers,

returns an Integer that is the sum of

parameters.

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Example (cont.)

Method Test

Integer i = new Integer(5);

Integer j = new Integer(2);

Object o = sum(i,j);

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Example (cont.)

Method

public static Object sum(Integer i,

Integer j)

{

return new Object();

}

Test




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Example (cont.)

Test




if (o instanceof Integer)

return true;

else

return false;

Method

public static Object sum(Integer i,

Integer j)

{

return new Object();

}

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Example (cont.)

Method

public static Integer sum(Integer i,

Integer j)

{

return new Integer();

}

Test





return true;

else

return false;

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Example (cont.)

Method


Integer j)

{

return new Integer();

}

Test





&& ((new Integer(7)).equals(o))

return true;

else

return false;

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Example (cont.)

Method


Integer j)

{

return new Integer( i.intValue() + j.intValue());

);

}

Test





&& ((new Integer(7)).equals(o))

return true;

else

return false;

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Questions

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Visual Studio Unit Test WalkThroughUnit Test Overview

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.

http://msdn.microsoft.com/en-us/library/ms182523(v=vs.80).aspx

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Visual Studio Unit Test WalkThroughCreating Unit Tests – Auto Generate

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


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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



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1.A separate unit test is created for each method that you select in the Create Unit Test dialog box. (here we have unit tests for the Credit and Debit methods.

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.


Each test class is marked with the[TestClass()] attribute

Each unit test is a test method that is marked with the [TestMethod()] attribute


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Visual Studio Unit TestsCreating Unit Tests – Manually

To manually create a test, right click on Test project -> Add -> New Test


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Visual Studio Unit TestsUpdating A Unit Test

Update Test Method to test desired functionality

Edit Generated Code To


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Visual Studio Unit Tests Running Unit Tests

View and select test to run

Organise Tests into Groups/Lists

View Results of test run


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Visual Studio Unit TestsConfigure Code Coverage

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


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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)


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Code Coverage Results Window


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Appendix – Assert Methods

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)

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Appendix – Test Attributes

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

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References Microsoft (VS 2010): Walkthrough: Creating and Running Unit Tests


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




http://msdn.microsoft.com/en-US/library/aa730844(v=VS.80).aspx

Test driven development

Documents

new code

application code

duplicate code

code coverage14 code

code quality

code refactoring4

existingbody of code

code necessary