Improve unit test coverage for src/display/display_utils.js

The `DOMCanvasFactory` class is now fully covered. Moreover, missing
cases for the `getFilenameFromUrl` function have been included.

Finally, `var` usage has been removed.

test/unit/display_utils_spec.js

@@ -12,13 +12,111 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+/* eslint no-var: error */
 
 import {
-  DOMSVGFactory, getFilenameFromUrl, isValidFetchUrl
+  DOMCanvasFactory, DOMSVGFactory, getFilenameFromUrl, isValidFetchUrl
 } from '../../src/display/display_utils';
 import isNodeJS from '../../src/shared/is_node';
 
 describe('display_utils', function() {
+  describe('DOMCanvasFactory', function() {
+    let canvasFactory;
+
+    beforeAll(function(done) {
+      canvasFactory = new DOMCanvasFactory();
+      done();
+    });
+
+    afterAll(function() {
+      canvasFactory = null;
+    });
+
+    it('`create` should throw an error if the dimensions are invalid',
+        function() {
+      // Invalid width.
+      expect(function() {
+        return canvasFactory.create(-1, 1);
+      }).toThrow(new Error('Invalid canvas size'));
+
+      // Invalid height.
+      expect(function() {
+        return canvasFactory.create(1, -1);
+      }).toThrow(new Error('Invalid canvas size'));
+    });
+
+    it('`create` should return a canvas if the dimensions are valid',
+        function() {
+      if (isNodeJS()) {
+        pending('Document is not supported in Node.js.');
+      }
+
+      const { canvas, context, } = canvasFactory.create(20, 40);
+      expect(canvas instanceof HTMLCanvasElement).toBe(true);
+      expect(context instanceof CanvasRenderingContext2D).toBe(true);
+      expect(canvas.width).toBe(20);
+      expect(canvas.height).toBe(40);
+    });
+
+    it('`reset` should throw an error if no canvas is provided', function() {
+      const canvasAndContext = { canvas: null, context: null, };
+
+      expect(function() {
+        return canvasFactory.reset(canvasAndContext, 20, 40);
+      }).toThrow(new Error('Canvas is not specified'));
+    });
+
+    it('`reset` should throw an error if the dimensions are invalid',
+        function() {
+      const canvasAndContext = { canvas: 'foo', context: 'bar', };
+
+      // Invalid width.
+      expect(function() {
+        return canvasFactory.reset(canvasAndContext, -1, 1);
+      }).toThrow(new Error('Invalid canvas size'));
+
+      // Invalid height.
+      expect(function() {
+        return canvasFactory.reset(canvasAndContext, 1, -1);
+      }).toThrow(new Error('Invalid canvas size'));
+    });
+
+    it('`reset` should alter the canvas/context if the dimensions are valid',
+        function() {
+      if (isNodeJS()) {
+        pending('Document is not supported in Node.js.');
+      }
+
+      const canvasAndContext = canvasFactory.create(20, 40);
+      canvasFactory.reset(canvasAndContext, 60, 80);
+
+      const { canvas, context, } = canvasAndContext;
+      expect(canvas instanceof HTMLCanvasElement).toBe(true);
+      expect(context instanceof CanvasRenderingContext2D).toBe(true);
+      expect(canvas.width).toBe(60);
+      expect(canvas.height).toBe(80);
+    });
+
+    it('`destroy` should throw an error if no canvas is provided', function() {
+      expect(function() {
+        return canvasFactory.destroy({});
+      }).toThrow(new Error('Canvas is not specified'));
+    });
+
+    it('`destroy` should clear the canvas/context', function() {
+      if (isNodeJS()) {
+        pending('Document is not supported in Node.js.');
+      }
+
+      const canvasAndContext = canvasFactory.create(20, 40);
+      canvasFactory.destroy(canvasAndContext);
+
+      const { canvas, context, } = canvasAndContext;
+      expect(canvas).toBe(null);
+      expect(context).toBe(null);
+    });
+  });
+
   describe('DOMSVGFactory', function() {
     let svgFactory;
 
@@ -50,8 +148,7 @@ describe('display_utils', function() {
         pending('Document is not supported in Node.js.');
       }
 
-      let svg = svgFactory.create(20, 40);
-
+      const svg = svgFactory.create(20, 40);
       expect(svg instanceof SVGSVGElement).toBe(true);
       expect(svg.getAttribute('version')).toBe('1.1');
       expect(svg.getAttribute('width')).toBe('20px');
@@ -73,25 +170,30 @@ describe('display_utils', function() {
         pending('Document is not supported in Node.js.');
       }
 
-      let svg = svgFactory.createElement('svg:rect');
-
+      const svg = svgFactory.createElement('svg:rect');
       expect(svg instanceof SVGRectElement).toBe(true);
     });
   });
 
   describe('getFilenameFromUrl', function() {
     it('should get the filename from an absolute URL', function() {
-      var url = 'http://server.org/filename.pdf';
-      var result = getFilenameFromUrl(url);
-      var expected = 'filename.pdf';
-      expect(result).toEqual(expected);
+      const url = 'https://server.org/filename.pdf';
+      expect(getFilenameFromUrl(url)).toEqual('filename.pdf');
     });
 
     it('should get the filename from a relative URL', function() {
-      var url = '../../filename.pdf';
-      var result = getFilenameFromUrl(url);
-      var expected = 'filename.pdf';
-      expect(result).toEqual(expected);
+      const url = '../../filename.pdf';
+      expect(getFilenameFromUrl(url)).toEqual('filename.pdf');
+    });
+
+    it('should get the filename from a URL with an anchor', function() {
+      const url = 'https://server.org/filename.pdf#foo';
+      expect(getFilenameFromUrl(url)).toEqual('filename.pdf');
+    });
+
+    it('should get the filename from a URL with query parameters', function() {
+      const url = 'https://server.org/filename.pdf?foo=bar';
+      expect(getFilenameFromUrl(url)).toEqual('filename.pdf');
     });
   });