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Info
You are going to follow a TDD approach to find the highest score for a series of topics

Given the following specification

...

An organisation delivers several topics (subjects). Students are graded against each topic. You are required to store the top score for each topic.

We’ve designed the application so that it comprises of three core classes:

A class to find the highest number from an array of integers.
A class to find the highest score for a topic.
A class to write the topic and score to a file on the disk.

...

Info
You are going to follow a TDD approach to find the highest score for a series of topics

Given the following specification

If the input is [{“Physics”, {56, 67, 45, 89}}], the result should be [{“Physics”, 89}]
If the input is [] the result should be []
If the input is [{“Physics”, {56, 67, 45, 89}}, {“Art”, {87, 66, 78}], the result should be [{“Physics”, 89}, {“Art”, 87}]
If the input is [{“Physics”, {56, 67, 45, 89}}, {“Art”, {87, 66, 78}}, {“Comp Sci”, {45, 88, 97, 56}}], the result should be [{“Physics”, 89}, {“Art”, 87}, {“Comp Sci”, 97}]

...

Create a new Test Project in the FindHighestNumber Solution
Install the packages you want (MSTest already installed, or NUnit - we are going to be using NUnit)
Create a new setup the new test class as shown here (remember you will have errors)

Code Block

language	c#

namespace TopicManagerTests
{
    public class TopicManagerTests
    {
        [Test]
        public void find_heighest_score_in_empty_array_return_empty_array()
        {
            // Arrange
            int[] array = {};
            TopicManager cut = new TopicManager();
            int[] expectedResult = {};

            // Act
            Topic[] result = cut.findTopicHighScores(array);

            // Assert
            Assert.That(result, Is.EqualTo(result));
        }
    }
}

Create a new class called TopicManager in the FindHighestNumberService project
Clean the code up so that the class is in a namespace called TopicManagerService
Lines 9, 11, and 14 give us enough information to allow us to start thinking about what we are trying to design here. based on the requirements, we want to pass into the method findTopicHighScores an array of Topics and their accompanying scores. It should return the topic score of each Topic, we will call this TopicTopScore. Each item in the array being passed into the findTopicHighScores will be called TopicScores (plural I know, but it matches the context, you may want to lose the ‘s' at the end of the class name). Let’s refactor the code to reflect what we have outlined here.

Code Block

language	c#

    public class TopicManagerTests
    {
        [Test]
        public void find_heighest_score_in_empty_array_return_empty_array()
        {
            // Arrange
            TopicScores[] array = Array.Empty<TopicScores>();
            TopicManager cut = new TopicManager();
            TopicTopScore[] expectedResult = Array.Empty<TopicTopScore>();

            // Act
            TopicTopScore[] result = cut.findTopicHighScores(array);

            // Assert
            Assert.That(result, Is.EqualTo(result));
        }
    }

We are now in a good position to get VS to generate the findTopicHighScores with the correct signature

Code Block

language	c#

namespace TopicManagerService
{
    public class TopicManager // TopicManager.cs
    {
        public TopicTopScore[] findTopicHighScores(TopicScores[] array)
        {
            // This block oc code assumes that the input is an empty array, there is no need for an if statement
            return Array.Empty<TopicTopScore>();
        }
    }
}

Now we need to complete the first piece of implementation code to pass the test
So you should have will also need the following pieces of code

Code Block
namespace TopicManagerService { public class TopicTopScore // TopicTopSscore.cs { } }

Code Block
namespace TopicManagerService { public class TopicScores // TopicScores.cs { } }

...

The HighestNumberFinder is designed to return an integer representing the number in a group of numbers. This can easily be stubbed out.Here is the Stub

Begin by creating a new test

Code Block

language	c#

namespace TopicManagerService
{[Test]
        public class HighestNumberFindervoid find_heighest_score_with_array_of_one_return_array_of_one_using_stub()
    {    {
    public int findHighestNumber(int[] values)     // Arrange
  {          int[] scores = return 89{ 56, 67, 45, 89 };
        }
    }
}

But when you try and use this class in the tests, you should see type errors. This is because, in the implementation unit of TopicManager, it's typed against HighestNumberFinder in a namespace called FindHighestNumberService.v6. So namespaces do not offer us the solution we are looking for.

Here are the modified tests

Code Block

language	c#

using NUnit.Framework;

namespace TopicManagerService
{
    public class TopicManagerTests
    {    string topicName = "Physics";
            TopicScores[] topicScores = { new TopicScores(topicName, scores) };
            IHighestNumberFinder hnf = new TopicManagerServiceStubs.HighestNumberFinder();
            TopicManager  [Test]cut = new TopicManager(hnf);
         public void find_heighest_score_in_empty_array_return_empty_array()
        { TopicTopScore[] expectedResult = { new TopicTopScore(topicName, 89) };

            // ArrangeAct
            TopicScoresTopicTopScore[] topicScoresresult = Arraycut.Empty<TopicScores>findTopicHighScores(topicScores);

           HighestNumberFinder hnf// =Assert
new HighestNumberFinder();             TopicManager cut = new TopicManager(hnfAssert.AreEqual(result[0].TopicName, expectedResult[0].TopicName);
            TopicTopScoreAssert.AreEqual(result[0].TopScore, expectedResult = Array.Empty<TopicTopScore>([0].TopScore);
        }
    // Act
}

Here is the Stub. We have put it in a different namespace in the test project

Code Block

language	c#

namespace TopicManagerServiceStubs
{
    public class HighestNumberFinder
    TopicTopScore[]{
 result = cut.findTopicHighScores(topicScores);     public int findHighestNumber(int[] values)
     // Assert  {
          Assert.That(result, Is.EqualTo(expectedResult))  return 89;
        }
         [Test]
        public void find_heighest_score_with_array_of_one_return_array_of_one()
        {
            // Arrange
            int[] scores = { 56, 67, 45, 89 };
            string topicName = "Physics";
            TopicScores[] topicScores = { new TopicScores(topicName, scores) };
     }
}

But when you try and use this class in the tests, you should see type errors in all the tests. This is because, in the implementation unit of TopicManager, it's typed against HighestNumberFinder in a namespace called FindHighestNumberService.v6. So namespaces do not offer us the solution we are looking for.

Here are the updated tests. Alternatively, you could modify TopicManager so it has a default constructor, but you will need to think about different issues and more tests for if TopicManager default constructor is used.

Code Block

language	c#

using NUnit.Framework;

namespace TopicManagerService
{
    public class TopicManagerTests
    {
        [Test]
      HighestNumberFinder hnf =public new HighestNumberFinder();void find_heighest_score_in_empty_array_return_empty_array()
        {
        TopicManager  cut = new TopicManager(hnf);// Arrange
            TopicTopScoreTopicScores[] expectedResulttopicScores = {new TopicTopScore(topicName, 89)}Array.Empty<TopicScores>();
            HighestNumberFinder //hnf Act= new HighestNumberFinder();
          TopicTopScore[] result = cut.findTopicHighScores(topicScoresTopicManager cut = new TopicManager(hnf);
            TopicTopScore[] expectedResult = Array.Empty<TopicTopScore>();

            // AssertAct
            Assert.AreEqual(resultTopicTopScore[0].TopicName, expectedResult[0].TopicName] result = cut.findTopicHighScores(topicScores);

           Assert.AreEqual(result[0].TopScore, expectedResult[0].TopScore // Assert
            Assert.That(result, Is.EqualTo(expectedResult));
        }

        }
}

Observe errors on lines 14 and 32.

We need to use interfaces. And the interface needs to be in a place that is available to both production code and tests.

...

Create a new interface that is part of the HighestNumberFinder project

...

language	c#

...

[Test]
        public void find_heighest_score_with_array_of_one_return_array_of_one()

...

       // Arrange

...

Copy HighestNumberFinder.v6 to HighestNumberFinderFinal and refactor the class so that it implements the interface above

...

language	c#

...

 int[]

...

scores

...

= { 56, 67, 45, 89

...

};

...

    string topicName =

...

"Physics";

...

 TopicScores[] topicScores = { new TopicScores(topicName, scores) };

...

 HighestNumberFinder

...

hnf

...

= new HighestNumberFinder();

...

TopicManager cut = new TopicManager(hnf);

...

      TopicTopScore[] expectedResult =

...

{new TopicTopScore(topicName, 89)};

            // Act

...

TopicTopScore[] result =

...

cut.findTopicHighScores(topicScores);

...

//

...

Assert

...

      Assert.AreEqual(result[0].TopicName, expectedResult[0].TopicName);

...

Assert.AreEqual(result[0].TopScore, expectedResult[0].TopScore);
        }

...

}
}

To give us more flexibility, we need to use an interface. And the interface needs to be in a place that is available to both production code and tests.

Create a new interface that is part of the HighestNumberFinder production project

Code Block

language	c#

namespace FindHighestNumberService
{
    public interface IHighestNumberFinder
    {
}        int findHighestNumber(int[] values);
  return result;
        }
    }
}

Refactor the tests so that the HighestNumberFinder is instantiated as follows

Code Block
IHighestNumberFinder hnf = new FindHighestNumberServiceFinal.HighestNumberFinder();

Refactor TopicManager so it now works with the interface IHighestNumberFinder and not directly with the implementation class
Rerun all your tests they should still be passing.

Tip
The tests have given us the confidence to refactor the code and begin to think more clearly about our implementation.

Now let’s substitute a stub in place of the real implementation of `HighestNumberFinder`.

Create a new called find_heighest_score_with_array_of_one_return_array_of_one_using_stub(), it's a copy of find_heighest_score_with_array_of_one_return_array_of_one()
Code Block
language c#
} }
Copy HighestNumberFinder.v6 to HighestNumberFinderFinal
Refactor the class so that it implements the interface above

Code Block

language	c#

using System;
using FindHighestNumberService;

namespace FindHighestNumberServiceFinal
{
    public class EmptyArrayException : Exception
    {
        public EmptyArrayException(string message):base(message)
        {
        }
    }
    public class HighestNumberFinder : IHighestNumberFinder
    {
        public int findHighestNumber(int[] values)
        {
            [Test]
 if (values.Length < 1)
      public void find_heighest_score_with_array_of_one_return_array_of_one_using_stub()        throw {new EmptyArrayException("Array is empty");

        // Arrange   int result = Int32.MinValue;

     int[] scores = { 56, 67, 45, 89for };(int i = 0; i < values.Length; i++)
     string topicName = "Physics";    {
        TopicScores[] topicScores = { new TopicScores(topicName, scores) }; if (values[i] > result)
        IHighestNumberFinder hnf = new FindHighestNumberServiceFinal.HighestNumberFinder();        result = values[i];
  TopicManager cut = new TopicManager(hnf);      }
      TopicTopScore[] expectedResult = { new TopicTopScore(topicName, 89) } return result;
        }
    // Act
 }
}

Modify the Stub version so it also implements IHighestNumberFinder
Refactor TopicManager so it now works with the interface IHighestNumberFinder and not directly with the implementation class

Code Block

language	c#

namespace TopicManagerServiceStubs
{
    public class TopicManager
   TopicTopScore[] result{
= cut.findTopicHighScores(topicScores);       private IHighestNumberFinder highestNumberFinder;

   // Assert    public  TopicManager( IHighestNumberFinder      Assert.AreEqual(result[0].TopicName, expectedResult[0].TopicName);hnf )
        {
    Assert.AreEqual(result[0].TopScore, expectedResult[0].TopScore);        highestNumberFinder = hnf;
 }       }

Modify line 8 to
Code Block
language c#
IHighestNumberFinder hnf = new TopicManagerService.HighestNumberFinder();
The error is because of TopicManagerTests
.
HighestNumberFinder does not implement the IHighestNumberFinder interface. Modify it so that it does.Rerun the tests, they should all pass
.
Rerun all your tests they should still be passing.

Tip
The tests have given us the confidence to refactor the code and begin to think more clearly about our implementation.

Info
We’ve now created a controlled environment for our tests

QLC-2.3 Limitations of Stubs, complete

...

this TopicManager

...

requirement

Add more tests to handle the last two requirements

•If the input is [{“Physics”, {56, 67, 45, 89}}, {“Art”, {87, 66, 78}], the result should be [{“Physics”, 89}, {“Art”, 87}]

Only one of the tests passes. Why?

Sample Solution

QLC-2.4 Mocks, complete the last TopicManager requirement

•If the input is [{“Physics”, {56, 67, 45, 89}}, {“Art”, {87, 66, 78}}, {“Comp Sci”, {45, 88, 97, 56}}], the result should be [{“Physics”, 89}, {“Art”, 87}, {“Comp Sci”, 97}]

Sample Solution

Versions Compared

Old Version 17

New Version Current

Key

Now let’s substitute a stub in place of the real implementation of `HighestNumberFinder`.

QLC-2.3 Limitations of Stubs, complete

this TopicManager

requirement

QLC-2.4 Mocks, complete the last TopicManager requirement

Page Comparison

Versions Compared

Old Version 17

New Version Current

Key

Now let’s substitute a stub in place of the real implementation of HighestNumberFinder.

QLC-2.3 Limitations of Stubs, complete

this TopicManager

requirement

QLC-2.4 Mocks, complete the last TopicManager requirement

Now let’s substitute a stub in place of the real implementation of `HighestNumberFinder`.