Better tests for getPixelColor.

test/screen.js

@@ -4,11 +4,31 @@ var pixelColor, screenSize;
 
 test('Get pixel color.', function(t) 
 {
-	t.plan(4);
+	t.plan(8);
 	t.ok(pixelColor = robot.getPixelColor(5, 5), 'successfully got pixel color.');
 	t.ok(pixelColor !== undefined, 'pixelColor is a valid value.');
 	t.ok(pixelColor.length === 6, 'pixelColor is the correct length.');
 	t.ok(/^[0-9A-F]{6}$/i.test(pixelColor), "pixelColor is valid hex.");
+
+	t.throws(function()
+	{
+		robot.getPixelColor(9999999999999, 9999999999999);
+	}, /outside the main screen/, 'get color of pixel (9999999999999, 9999999999999).');
+
+	t.throws(function()
+	{
+		robot.getPixelColor(-1, -1);
+	}, /outside the main screen/, 'get color of pixel (-1, -1).');
+
+	t.throws(function()
+	{
+		robot.getPixelColor(0);
+	}, /Invalid number/, 'get color of pixel (0).');
+
+	t.throws(function()
+	{
+		robot.getPixelColor(1, 2, 3);
+	}, /Invalid number/, 'get color of pixel (1, 2, 3).');
 });
 
 test('Get screen size.', function(t)