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

...

• If the input were {4, 5, -8, 3, 11, -21, 6} the result should be 11

• An empty array should throw an exception

• A single-item array should return the single item

• If several numbers are equal and highest, only one should be returned

• If the input were {7, 13}  then the result should be 13

• If the input were {13, 4}  then the result should be 13

Steps

1. Begin by creating a solution called FindHighesNumber with a testing project called FindHighestNumberTests (use the NUnit testing framework)Rename the test new maven project called HighesNumberServices

2. Create a package in the test folder called com.demos.findhighestnumber

3. Create a test class called to HighestNumberFinderTests

4. The most challenging part is determining which test to write first.  Always start simple and with a test that will not need to handle exceptions.

   • So the simplest test we could do here is

     • A single-item array should return the single item

     • Write this first test, let’s call the test method array_of_one_item_returns_this_item()

     • Code Block
       language c#	java
       package com.s2s.demos.findhighestnumber.v1; import org.junit.Test; import static org.junit.Assert.*; /** * * @author selvy */ public class HighestNumberFinderTest { // TODO add test methods here. // The methods must be annotated with annotation @Test. For example: [Test]// @Test public void Arrayfind_highest_in_array_of_one_itemexpect_returns_thissingle_item() { { // Arrange // Arrange int array[] = int[] values = { 33 }; 10 int expectedResult = 33; }; HighestNumberFinder cut = new HighestNumberFinder(); int expectedResult = 10; // Act // Act int result = cut.findHighestNumber(values array ); // Assert assertEquals( Assert.That(result, Is.EqualTo(expectedResult)expectedResult, result ); } }

5. Create a new project called FindHighestNumberService in the same solution

6. Rename the production class to HighestNumberFinder

7. Depending on the IDE you are using, most will allow you to create a class or method that doesn’t currently exist. In the Test file HighestNumberFinderTests, try right-click clicking on the HighestNumberFinder declaration and select Add reference to HighestNumberFinder, the error should disappear

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   In the Test file HighestNumberFinderTests, right-click on the method findHighestNumber() and select Generate method

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   and and see if there is an option to create the missing class. Make sure to create the class in the src folder and not the test folder

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    Try the same technique to create the method

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    Following a TDD approach, we get the IDE generate the production methods that match the tests

12. Now begin to work on the production code

    • Write enough production code to pass the test.

      • Do not be tempted to try and answer other parts of the requirements. Focus only on this requirement “A single item array should return the single item”

      • Code Block
        language c#
        using System; namespace FindHighestNumberService { public class HighestNumberFinder { public int findHighestNumber(int[] valuesarray) { return valuesarray[0]; } } }

      • Make sure the test passes

      • A Golden rule of TDD - if this was the only requirement then you have completed your task. Only write enough code to pass the test.

      • Commit your passing code to your git repo (never commit broken code)

13. Select the next requirement

    • I would suggest this one - If the input were {13, 4}  then the result should be 13

      • Write the second test, let’s call the test method array_of_two_descending_items_return_first_item()

      • Code Block
        language c#
        @Test [Test] public void public void Arrayfind_highest_in_array_of_two_descending_itemsexpect_return_first_itemelement() { // Arrange int intarray[] values = { 13, 4 }; int expectedResult = 13; HighestNumberFinder cut = new HighestNumberFinder(); // Act // Act int result = cut.findHighestNumber(valuesarray); //Assert // Assert Assert.That(result, Is.EqualTo(expectedResult)); assertEquals(expectedResult, result); }

      • Write enough production code to pass the test. In this edge case, the production code does not change

      • Make sure the test passes

      • Commit your passing code to your git repo (never commit broken code)

14. Select the next requirement

    • I would suggest - If the input were {7, 13}  then the result should be 13

      • Write the third test, let’s call the test method array_of_two_ascending_items_return_last_item()

      • Code Block
        language c#
        [Test] public void Array_of_two_ascending_items_return_last_item() { // Arrange int[] values = { 7, 13 }; int expectedResult = 13; HighestNumberFinder cut = new HighestNumberFinder(); // Act int result = cut.findHighestNumber(values); //Assert Assert.That(result, Is.EqualTo(expectedResult)); }

      • Write enough production code to pass the test. Do not be tempted to try and answer the parts of the requirements. Focus only on this requirement “If the input were {7, 13}  then the result should be 13”

      • Code Block
        language c#
        public int findHighestNumber(int[] valuesarray) { int resulthighestSoFar = valuesarray[0]; if( (valuesarray.Lengthlength > 1 && valuesarray[1] > resulthighestSoFar ) highestSoFar result = valuesarray[1]; return result; return highestSoFar; }

    • Make sure the test passes

    • Commit your passing code to your git repo (never commit broken code)

    • The Production code has changed. Does it need to be refactored?

      • if yes, refactor the code

    • Make sure the test still passes

    • Commit your passing code to your git repo (never commit broken code)

15. Select each requirement and implement the test first then the production code