Firebase mock: started new implementation

__mocks__/__tests__/gatsby-plugin-firebase_2.test.js

@@ -0,0 +1,45 @@
+import FirebaseMock from '../gatsby-plugin-firebase_2';
+
+describe('database', () => {
+  it('reuses existing Database instance', async () => {
+    const database1 = FirebaseMock.database();
+    const database2 = FirebaseMock.database();
+
+    expect(database1.uuid).toBeTruthy();
+    expect(database2.uuid).toBeTruthy();
+    expect(database1.uuid).toEqual(database2.uuid);
+  });
+
+  it('reuses existing Reference instance', async () => {
+    const ref1 = FirebaseMock.database().ref('resumes/123');
+    const ref2 = FirebaseMock.database().ref('resumes/123');
+
+    expect(ref1.uuid).toBeTruthy();
+    expect(ref2.uuid).toBeTruthy();
+    expect(ref1.uuid).toEqual(ref2.uuid);
+  });
+
+  it('ServerValue.TIMESTAMP returns current time in milliseconds', async () => {
+    const now = new Date().getTime();
+    const timestamp = FirebaseMock.database.ServerValue.TIMESTAMP;
+
+    expect(timestamp).toBeTruthy();
+    expect(timestamp).toBeGreaterThanOrEqual(now);
+  });
+
+  it("can spy on Reference 'update' function", async () => {
+    const referencePath = 'resumes/123456';
+    const functionSpy = jest.spyOn(
+      FirebaseMock.database().ref(referencePath),
+      'update',
+    );
+    const updateArgument = 'test value 123';
+
+    await FirebaseMock.database().ref(referencePath).update(updateArgument);
+
+    expect(functionSpy).toHaveBeenCalledTimes(1);
+    const functionCallArgument = functionSpy.mock.calls[0][0];
+    expect(functionCallArgument).toBeTruthy();
+    expect(functionCallArgument).toEqual(updateArgument);
+  });
+});