Added repositories, made database unit-testable.

backend/tests/example.test.ts

@@ -4,6 +4,6 @@ describe("Sample test", () => {
     it("should sum to 2", () => {
         const expected = 2;
         const result = 1 + 1;
-        expect(result).toBe(expected);
+        expect(result).equals(expected);
     });
 })