The Scroll Test


You can start a new test class in a number of ways. Lee Holmes of Microsoft uses a keyboard macro to convert a new class file into a test class. See my Web site for an article about how to build a new template for a test class and install it into Microsoft Visual Studio. Often I just manually edit a new class, and I often write a first test that just runs trivially so that I can be sure that it is hooked up:

 using System; 
using NUnit.Framework;
namespace Notepad
{
[TestFixture] public class TestScroll: Assertion
{
[Test] public void HookUp() {
Assert("hooked up", true);
}
}
}

Once that works ”and it does ”I ll proceed to write the test I actually want:

 [Test] public void ScrollHappens() { 
MockTextBox mock = new MockTextBox();
XMLNotepad notepad = new XMLNotepad();
Assert("no scroll", !mock.Scrolled);
notepad.PutText(mock, lines, selectionStart);
Assert("scroll happens", mock.Scrolled);
}

I just sketched my intention here, and look what happened . I want to set up a MockTextBox, have it declare that it isn t scrolled, then put some text into it, and have it respond that now it is scrolled. My idea is that the MockTextBox will just set a flag when sent the ScrollToCaret. But look at the PutText message. I realized that I don t want to go through the Form if I don t have to, because the Form is doing all kinds of things to the model and textbox that I can t control. So I want not only the textbox parameter but also the lines and selectionStart to be parameters as well.

The test is telling me things about how the object should work.

However, I m getting in a bit deep here. It s time to dig out and make sure things are running. I m going to comment out a few lines of this test and then get it running:

 [Test] public void ScrollHappens() { 
MockTextBox mock = new MockTextBox();
// XMLNotepad notepad = new XMLNotepad();
Assert("no scroll", !mock.Scrolled);
// notepad.PutText(mock, lines, selectionStart);
// Assert("scroll happens", mock.Scrolled);
}

So I write a quick MockTextObject:

 using System; 
namespace Notepad
{
public class MockTextBox
{
public MockTextBox()
{
}
public Boolean Scrolled {
get {
return false;
}
}
}
}

That test runs. Now I ll uncomment the commented test lines and get to work. The program doesn t compile because lines and selectionStart aren t defined. We can fix that:

 [Test] public void ScrollHappens() { 
int selectionStart = 1;
string[] lines = new String[] { "hello", "world" };
MockTextBox mock = new MockTextBox();
XMLNotepad notepad = new XMLNotepad();
Assert("no scroll", !mock.Scrolled);
notepad.PutText(mock, lines, selectionStart);
Assert("scroll happens", mock.Scrolled);
}

The compiler tells us that no overload for method PutText() takes three arguments. We knew that; that s what we are here to fix. So Back to XMLNotepad to fix PutText:

 void XMLKeyDownHandler(object objSender, KeyEventArgs kea) { 
model.SetLines(textbox.Lines);
model.SelectionStart = textbox.SelectionStart;
if (kea.KeyCode == Keys.Enter) {
model.Enter();
kea.Handled = true;
}
PutText(textbox, model.LinesArray(), model.SelectionStart);
}
public void PutText(TextBox textbox, string[] lines, int selectionStart) {
textbox.Lines = lines;
textbox.SelectionStart = selectionStart;
textbox.ScrollToCaret(); // keep cursor on screen. no test.
}

This nearly works, except (of course) that MockTextBox isn t a TextBox. I m tempted to have it subclass TextBox, but that s not likely to be a good idea: it would be inheriting lots of behavior that I don t understand, and the PutText method would be sending it messages. Instead, I m going to comment out the line that sends to it, and I ll test the GUI manually to be sure my new PutText is working. And it seems to be. The next step shouldn t be too hard, but it s a bit of a big one.




Extreme Programming Adventures in C#
Javaв„ў EE 5 Tutorial, The (3rd Edition)
ISBN: 735619492
EAN: 2147483647
Year: 2006
Pages: 291

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