 The first bit of programming we
can do is for the PIA class. We know that we need to simulate the hardware and we know what that needs to look
like. There will be 3 methods, one for programming the input and output bits, one to read, and one to write to
the PIA. So let's create the PIA first.
The way that we create code in Extreme
Programming (XP) is to start with a test. |
Fortunately we have already created a unit testing framework. So lets create some code
for our first test. What we want here is to be able to read the PIA and have any bits programmed to output always
be zero. Input bits are unaffected when being read. |
package simulator.r1.unittest;
import unittest.framework.*;
import simulator.r1.*;
public class TestReadFromPIA extends Test
{public void runTest()
{PIA.register = 0x0F0F;
PIA.setInputs(0x00FF);
should(PIA.read() == 0x000F, "Outputs
should always be zero");};}
|
| To be able to compile and run this
test we need to create a stub class for our PIA. We will just create the methods and not bother writing code. |
|
package simulator.r1;
public class PIA
{public static int register;
public static int read()
{return 0x0000;}
public static void setInputs(int
aShort)
{};}
|
| Next we can create a TestSuite for
our first test. |
|
package simulator.r1.unittest;
import unittest.framework.*;
public class SimulatorTests extends TestSuite
{public SimulatorTests()
{tests = new Test[1];
tests[0] = new TestReadFromPIA();};}
|
| Now we can run this test. It fails
of course. But we like to run it to make sure. Occasionally the test will pass, which means that our code already
does what we need or our test doesn't test what we need. Lets go back to the PIA class and write some code to make
the test work. We add some code and get the following. |
|
package simulator.r2;
class PIA
{public static int register = 0;
public static int inputBits = 0;
public static int read()
{return register & inputBits;}
public static void setInputs(int
aBitMask)
{inputBits = aBitMask;};}
|
Let's try the unit test now. It
runs as expected. Our code is still nice and simple and clean so we don't need to refactor. So let's add a second
test. We need to test writing
to the PIA. |
|
