QL-4.1) Phase 1

Create a new test class called LiveFileLoaderTest.

Write the unit test first for a CUT called FileLoader.  It should only have one public method on it.  Once the test is written develop the CUT to pass the test.

public int loadFile(string fname)

Once you have completed the above test and production code, think about this question

• Question: What’s the weakness of this design

A solution can be found here

QL-4.2) Phase 2

Create a new test class called FileLoaderTest.

Write the unit test first for a CUT called FileLoader.  It should only have a new public method on it.  Once the test is written develop the CUT to pass the test.

In order to facilitate your design, you need to think about the structure of the test

1. In the //Act part of the test, we want to write something like this

2.         // act
           int bytesRead = cut.loadFile((fname) ->
           {
              List<String> result = null;
              try
              {
                  result = Files.readAllLines(Paths.get(fname), StandardCharsets.UTF_8);
              }
              catch (IOException e){}
              return result;
           });

3. Reading the API guides we see that File.readAllLines() returns a List<string>, so let's change the code to match this

4. package com.celestial.mockito.filetodb;
   
   import java.io.IOException;
   import java.nio.charset.StandardCharsets;
   import java.nio.file.Files;
   import java.nio.file.Paths;
   import java.util.ArrayList;
   import java.util.List;
   import static org.junit.jupiter.api.Assertions.assertEquals;
   import org.junit.jupiter.api.Test;
   import org.mockito.MockedStatic;
   import org.mockito.Mockito;
   
   public class FileLoaderTest 
   {
       // Redesign the FileLoader so that the machenism to load files up can be 
       // passed in as a lambda - still titghtly coupled the file system
       @Test
       public void load_all_of_file_using_inbuilt_Files_type_as_lambda() 
       {
           // arrange
           String fileToLoad = "c:/tmp/KeyboardHandler.txt";
           FileLoader cut = new FileLoader(fileToLoad);
           int expectedBytesRead = 10;    //1371;
           List<String> pretendFileContent = new ArrayList<>();
           pretendFileContent.add("Hello");
           pretendFileContent.add("world");
           MockedStatic<Files> ff = Mockito.mockStatic(Files.class);
           ff.when(() -> Files.readAllLines(Paths.get(fileToLoad), StandardCharsets.UTF_8)).thenReturn(pretendFileContent);
   
           // act
           int bytesRead = cut.loadFile((fname) ->
           {
              List<String> result = null;
              try
              {
                  result = Files.readAllLines(Paths.get(fname), StandardCharsets.UTF_8);
              }
              catch (IOException e){}
              return result;
           });
   
           // assert
           assertEquals(expectedBytesRead, bytesRead);
       }
   }

5. At line 32, we are using Mockito’s mockStatic() to mock a Static class

6. At line 33, we setup the expectation

7. So we need to design a loadFile() method that takes as a parameter a block of code that can read the file from any source.

8. public int LoadFile(string fname, ILoadFile func)

9. Create a new interface called

10. package com.celestial.mockito.filetodb;
    
    import java.util.List;
    
    /**
     *
     * @author selvy
     */
    @FunctionalInterface
    public interface ILoader 
    {
        List<String>    loadFile(String fname);
    }

11. Modify FileLoader so it has this additional functionality

12.     public List<String> getLines() {
            return lines;
        }
        
        int loadFile(ILoader func) 
        {
            lines = func.loadFile(fileToLoad);
            return calculateFileSize();
        }    
    ...

Once you have completed the above test and production code, think about this question

• Question: What’s the weakness of this design

A solution can be found here

QL-4.3) Phase 3 - working stubs

The phase 2 test was weakened by the fact that It broke one of the tenants o a good test

• A test should not make any IO calls

Because we have designed the FileLoader so that a lambda can be passed in, we can rethink what the test should look like.

Create a new test that specifically targets using canned data.

In the //Act part of the test redesign the lambda expression so that it returns a list of strings.

You should not have to change the CUT.

Once you have completed the above test and production code, think about this question

• Question: Can we further improve the test

A solution can be found here

QL-4.4) Phase 4 - working with mocks

In this implementation of the test System.IO.File object. But wait, System.IO.File.ReadLines() is a class-level operation and not an object-level operation. Most mocking frameworks struggle with mocking class-level methods.

We are going to use a mocking library called Mockito (you saw it being used earlier). It’s one of the more popular mocking libraries for Java code

Begin by writing your test in the normal way

        // arrange
        string fileToLoad = "c:/tmp/KeyboardHandler.java.txt";
        FileLoader cut = new FileLoader();
        // setup ur canned data, these will represent the lines in the file
        List<string> pretendFileContent = new();
        pretendFileContent.Add("Hello");
        pretendFileContent.Add("world");
        int expectedBytesRead = 10;

Because java.io.File is a static class, this time we will create our own dummy interface with the required methods for our tests and CUT

Create this file in tests folder and not the production folder

package com.celestial.mockito.filetodb;

import java.nio.charset.Charset;
import java.nio.file.Path;
import java.util.List;

public interface MyFile
{
   public List<String> readAllLines(Path path, Charset cs); 
}

In our test, we can now mock this interface and set the expectations for the required method

        // Mock the interface
        MyFile file = mock(MyFile.class);
        
        // Setup the expectation
        when(file.readAllLines(Paths.get(fileToLoad), StandardCharsets.UTF_8)).thenReturn(pretendFileContent);

Line 2 creates a skeletal object of the MyFile interface.

Line 5 tells the mocked object that when the method readAllLines() is invoked the parameter value given in fileToRead, it should return the object pretendFileContent. We will look at this more closely in a short while.

Now in the //Act part of the test add the following code

        // act
        int bytesRead = cut.loadFile((fname) ->
        {
            List<String> result = file.readAllLines(Paths.get(fname), StandardCharsets.UTF_8);

            return result;
        });

In the lambda’s body, we simply invoke file.readAllLines(...). This is using the mocked object and mocked method we previously set up.

The Assert statement should be no different from the previous Assert statements in the other tests.

Run the test.

A solution can be found here

Do expectation parameters really matter?

Let’s look at the code

        // arrange
        String fileToLoad = "c:/tmp/KeyboardHandler.java.txt";
        FileLoader cut = new FileLoader( fileToLoad );
        ...
        ...        
        // Mock the interface
        MyFile file = mock(MyFile.class);
        
        // Setup the expectation
        when(file.readAllLines(Paths.get(fileToLoad), StandardCharsets.UTF_8)).thenReturn(pretendFileContent);
        
        // act
        int bytesRead = cut.loadFile((fname) ->
        {
            List<String> result = file.readAllLines(Paths.get(fname), StandardCharsets.UTF_8);

            return result;
        });

Change line 15 to (we’ve passed in XYZ as the file name)

                List<String> result = file.readAllLines(Paths.get("XYZ""), StandardCharsets.UTF_8);

Rerun the test and see what happens. It should fail.

When you set up an expectation on a mock object, you are not just specifying what method will be called, you are stating what values will be passed in as parameters to that method, and what value should be returned if those values match what you have said. In other words, if when the test is run the test values match the expected values, then the value you have stated will be returned. This is why it is called setting up the expectations.