Updated tests for fillText to better account for off-by-one errors.

tests/html/canvasrenderingcontext2d_test.dart

Index: tests/html/canvasrenderingcontext2d_test.dart
diff --git a/tests/html/canvasrenderingcontext2d_test.dart b/tests/html/canvasrenderingcontext2d_test.dart
index 32beb1e6ae8781458db435d68a43f60ea8659320..9cafb0d8c9f5296b077b44dadae515133c010ea5 100644
--- a/tests/html/canvasrenderingcontext2d_test.dart
+++ b/tests/html/canvasrenderingcontext2d_test.dart
@@ -679,25 +679,28 @@ main() {
     setUp(setupFunc);
     tearDown(tearDownFunc);
 
+    final x = 20;
+    final y = 20;
+
     test('without maxWidth', () {
       context.font = '40pt Garamond';
       context.fillStyle = 'blue';
 
       // Draw a blue box.
-      context.fillText('█', 50, 50);
+      context.fillText('█', x, y);
 
       var width = context.measureText('█').width;
 
-      checkPixel(readPixel(50, 50), [0, 0, 255, 255]);
-      checkPixel(readPixel(60, 50), [0, 0, 255, 255]);
+      checkPixel(readPixel(x, y), [0, 0, 255, 255]);
+      checkPixel(readPixel(x + 10, y), [0, 0, 255, 255]);
 
-      expectPixelUnfilled(40, 50);
-      expectPixelFilled(50, 50);
-      expectPixelFilled(60, 50);
+      expectPixelUnfilled(x - 10, y);
+      expectPixelFilled(x, y);
+      expectPixelFilled(x + 10, y);
 
       // The box does not draw after `width` pixels.
-      expectPixelFilled(50 + width, 50);
-      expectPixelUnfilled(50 + width + 1, 50);
+      expectPixelFilled(x + width - 1, y);
+      expectPixelUnfilled(x + width + 1, y);
     });
 
     test('with maxWidth null', () {
@@ -705,38 +708,40 @@ main() {
       context.fillStyle = 'blue';
 
       // Draw a blue box with null maxWidth.
-      context.fillText('█', 50, 50, null);
+      context.fillText('█', x, y, null);
 
       var width = context.measureText('█').width;
 
-      checkPixel(readPixel(50, 50), [0, 0, 255, 255]);
-      checkPixel(readPixel(60, 50), [0, 0, 255, 255]);
+      checkPixel(readPixel(x, y), [0, 0, 255, 255]);
+      checkPixel(readPixel(x + 10, y), [0, 0, 255, 255]);
 
-      expectPixelUnfilled(40, 50);
-      expectPixelFilled(50, 50);
-      expectPixelFilled(60, 50);
+      expectPixelUnfilled(x - 10, y);
+      expectPixelFilled(x, y);
+      expectPixelFilled(x + 10, y);
 
       // The box does not draw after `width` pixels.
-      expectPixelFilled(50 + width, 50);
-      expectPixelUnfilled(50 + width + 1, 50);
+      expectPixelFilled(x + width - 1, y);
+      expectPixelUnfilled(x + width + 1, y);
     });
 
     test('with maxWidth defined', () {
       context.font = '40pt Garamond';
       context.fillStyle = 'blue';
 
+      final maxWidth = 20;
+
       // Draw a blue box that's at most 20 pixels wide.
-      context.fillText('█', 50, 50, 20);
+      context.fillText('█', x, y, maxWidth);
 
-      checkPixel(readPixel(50, 50), [0, 0, 255, 255]);
-      checkPixel(readPixel(60, 50), [0, 0, 255, 255]);
+      checkPixel(readPixel(x, y), [0, 0, 255, 255]);
+      checkPixel(readPixel(x + 10, y), [0, 0, 255, 255]);
 
       // The box does not draw after 20 pixels.
-      expectPixelUnfilled(40, 50);
-      expectPixelUnfilled(71, 50);
-      expectPixelUnfilled(90, 50);
-      expectPixelFilled(50, 50);
-      expectPixelFilled(60, 50);
+      expectPixelUnfilled(x - 10, y);
+      expectPixelUnfilled(x + maxWidth + 1, y);
+      expectPixelUnfilled(x + maxWidth + 20, y);
+      expectPixelFilled(x, y);
+      expectPixelFilled(x + 10, y);
     });
   });
 }