Backfill WebAnnotation tests

__tests__/WebAnnotation.test.js

+import WebAnnotation from '../src/WebAnnotation';
+
+/** */
+function createSubject(args = {}) {
+  return new WebAnnotation({
+    body: 'body',
+    canvasId: 'canvasId',
+    id: 'id',
+    svg: 'svg',
+    xywh: 'xywh',
+    ...args,
+  });
+}
+
+describe('WebAnnotation', () => {
+  let subject = createSubject();
+  describe('constructor', () => {
+    it('sets instance accessors', () => {
+      ['body', 'canvasId', 'id', 'svg', 'xywh'].forEach((prop) => {
+        expect(subject[prop]).toBe(prop);
+      });
+    });
+  });
+  describe('target', () => {
+    it('with svg', () => {
+      expect(subject.target()).toEqual({
+        id: 'canvasId',
+        selector: {
+          type: 'SvgSelector',
+          value: 'svg',
+        },
+      });
+    });
+    it('with xywh only', () => {
+      subject = createSubject({ svg: null });
+      expect(subject.target()).toBe('canvasId#xywh=xywh');
+    });
+    it('with no xywh or svg', () => {
+      subject = createSubject({ svg: null, xywh: null });
+      expect(subject.target()).toBe('canvasId');
+    });
+  });
+  describe('toJson', () => {
+    it('generates a WebAnnotation', () => {
+      expect(subject.toJson().type).toBe('Annotation');
+    });
+  });
+});