1 files changed, 72 insertions, 0 deletions
diff --git a/spec/frontend/diff_spec.js b/spec/frontend/diff_spec.js
new file mode 100644
index 00000000000..759ae32ac51
--- /dev/null
+++ b/spec/frontend/diff_spec.js
@@ -0,0 +1,72 @@
+import createEventHub from '~/helpers/event_hub_factory';
+
+import Diff from '~/diff';
+
+describe('Diff', () => {
+  describe('diff <-> tabs interactions', () => {
+    let hub;
+
+    beforeEach(() => {
+      hub = createEventHub();
+    });
+
+    describe('constructor', () => {
+      it("takes in the `mergeRequestEventHub` when it's provided", () => {
+        const diff = new Diff({ mergeRequestEventHub: hub });
+
+        expect(diff.mrHub).toBe(hub);
+      });
+
+      it('does not fatal if no event hub is provided', () => {
+        expect(() => {
+          new Diff(); /* eslint-disable-line no-new */
+        }).not.toThrow();
+      });
+
+      it("doesn't set the mrHub property if none is provided by the construction arguments", () => {
+        const diff = new Diff();
+
+        expect(diff.mrHub).toBe(undefined);
+      });
+    });
+
+    describe('viewTypeSwitch', () => {
+      const clickPath = '/path/somewhere?params=exist';
+      const jsonPath = 'http://test.host/path/somewhere.json?params=exist';
+      const simulatejQueryClick = {
+        originalEvent: {
+          target: {
+            getAttribute() {
+              return clickPath;
+            },
+          },
+          preventDefault: jest.fn(),
+          stopPropagation: jest.fn(),
+        },
+      };
+
+      it('emits the correct switch view event when called and there is an `mrHub`', async () => {
+        const diff = new Diff({ mergeRequestEventHub: hub });
+        const hubEmit = new Promise((resolve) => {
+          hub.$on('diff:switch-view-type', resolve);
+        });
+
+        diff.viewTypeSwitch(simulatejQueryClick);
+        const { source } = await hubEmit;
+
+        expect(simulatejQueryClick.originalEvent.preventDefault).toHaveBeenCalled();
+        expect(simulatejQueryClick.originalEvent.stopPropagation).toHaveBeenCalled();
+        expect(source).toBe(jsonPath);
+      });
+
+      it('is effectively a noop when there is no `mrHub`', () => {
+        const diff = new Diff();
+
+        expect(diff.mrHub).toBe(undefined);
+        expect(() => {
+          diff.viewTypeSwitch(simulatejQueryClick);
+        }).not.toThrow();
+      });
+    });
+  });
+});