Add Canvas nullcheck to render function

lib/components/simulation_component.dart

@@ -25,8 +25,9 @@ class SimulationComponent implements OnInit {
     canvas.context2D.fillRect(0, 0, canvas.width, canvas.height);
     canvas.context2D.setFillColorRgb(0, 255, 0);
     canvas.context2D.fillText('''
-    If you see this\n
-    the app is broken :(
+    If you see this
+    
+    the canvas did not load correctly :(
     ''', canvas.width / 2 - 50, canvas.height / 2);
 //    engineService.create(canvas);
   }

lib/src/Engine.dart

@@ -22,7 +22,7 @@ class Engine {
   num _updateLag = 0.0;
   num _drawLag = 0.0;
 
-  final html.CanvasElement canvas;
+  html.CanvasElement canvas;
   Grid _grid = new Grid(GRID_X, GRID_Y);
   bool running = false;
 
@@ -43,7 +43,7 @@ class Engine {
   }
 
   void clear() {
-    _grid = new Grid(100, 100);
+    _grid = new Grid(GRID_X, GRID_Y);
     running = false;
   }
 
@@ -78,8 +78,7 @@ class Engine {
   }
 
   void render([num interp]) {
-//    print("rendering");
-    _grid.render(canvas, interp);
+    if(canvas != null) _grid.render(canvas, interp);
   }
 
   void addPattern(

test/src/engine_test.dart

@@ -1,12 +1,22 @@
 @TestOn('browser')
 
-import 'dart:html';
-
 import 'package:rules_of_living/src/Engine.dart';
 import 'package:test/test.dart';
 
 void main() {
   test("Engine can be instantiated without canvas", () {
-    expect(Engine(), isNot(throwsA(anything)));
+    expect(Engine(), isNot(throwsNoSuchMethodError));
+  });
+
+  test("Engine does not throw errors when calling render directly", () {
+    Engine sut = new Engine();
+    // anonymous function necessary since throws can not use functions with args
+    expect(() => sut.render(), isNot(throwsNoSuchMethodError));
+  });
+
+  test("Engine does not throw errors when processing without attached canvas", () {
+    Engine sut = new Engine();
+    // anonymous function necessary since throws can not use functions with args
+    expect(() => sut.process(1000), isNot(throwsNoSuchMethodError));
   });
 }