TDD FileLoader v1.4.

Using mocking in the test
The Unit Test
     @Test
     public void load_all_of_file_using_mock()
     {
        // arrange
        String fileToLoad = "c:/tmp/KeyboardHandler.java.txt";
        FileLoader cut = new FileLoader( fileToLoad );
        // setup ur canned data, these will represent the lines in the file
        ArrayList<String> pretendFileContent = new ArrayList<>();
        pretendFileContent.add("Hello");
        pretendFileContent.add("world");
        int expectedBytesRead = 10;
        
        // 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;
        });
        
         // assert
         assertEquals(expectedBytesRead, bytesRead);        
     }