QLC-2) Find the Highest Number Extension.

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.

Open

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}]

QLC-2.1) Setup and first test

1. In FindHighestNumber project create a new package that ends with .topicmanager

2. Create a new setup the new test class as shown here (remember you will have errors)

3. package xx.yy.zz.topicmanagerservice 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)); } }

4. Create a new class called TopicManager in the FindHighestNumberService project

5. Clean the code up so that the class is in a package called topicmanagerservice

6. 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 top 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.

7. public class TopicManagerTests { @Test public void find_heighest_score_in_empty_array_return_empty_array() { // Arrange ArrayList<TopicScores> array = new ArrayList<>(); TopicManager cut = new TopicManager(); ArrayList<TopicTopScore> expectedResult = new ArrayList<>(); // Act ArrayList<TopicTopScore> result = cut.findTopicHighScores( array ); // Assert assertEquals( expectedResult, result ); } }

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

9. class TopicManager { ArrayList<TopicTopScore> findTopicHighScores(ArrayList<TopicScores> array) { return new ArrayList<>(); } }

10. Now we need to complete the first piece of implementation code to pass the test

11. So you will also need the following pieces of code

Second test

1. Implement this second test

3. And here is the implementation class

5. Updated TopicScores.java

7. Updated TopicTopScores.java

9. Looking back at TopicManager, Line 3 represents the elephant in the code

   1. We already have tests for the HighestNumberFinder class, and yes class TopicManager requires HighestNumberFinder. But the coupling between these two classes is such that we cannot test TopicManger independently of HighestNumberFinder. Actually, this is a code smell.

   2. we can not substitute out HighestNumberFinder, this also is a code smell.

   3. We can remove the code smell by injecting HighestNumberFinder into TopicManager, when TopicManager is created.

10. Modify TopicManager as follows

    1. remove the creation of HighestNumberFinder at line 5

    2. Pass an instance of a HighestNumberFinder into TopicManager as a constructor parameter

12. Refactor the tests so that they run. You should not have to change any of the test data.

QLC-2.2) Working with Stubs

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

Begin by creating a new test

Here is the Stub you will use (create it in the test folder - it’s not production code)

The stub is substituted in line 11.

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, is typed against com.s2s.demos.findhighestnumber.fin.HighestNumberFinder. So packages do not offer us the solution we are looking for.

We need to use interfaces. 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.

1. Create a new interface that is part of the production code, and create it in the com.s2s.demos.findhighestnumber package

3. Modify the production version and test version of HighestNumberFinder, so that they both implement the interface IHighestNumberFinder

4. Here is the stub version

6. Here is the production version

8. Refactor TopicManager so it now works with the interface IHighestNumberFinder and not directly with the implementation class

10. You should find that the test is no longer in an error state

11. Rerun all your tests they should still be passing.

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}]