Issue #4: add frontend unit tests

src/utils.test.ts

@@ -0,0 +1,20 @@
+import { extractJsonPayload } from "utils"; 
+
+describe('Test utils.extractJsonPayload', () => {
+    it('Extract valid JSON', () => {
+      const result = extractJsonPayload('Hey {"foo": "bar"}')
+      expect(result).toEqual({
+        foo: "bar"
+      });
+    });
+
+    it('Extract non valid JSON', () => {
+        const result = extractJsonPayload('Hey {"foo": invalid}')
+        expect(result).toEqual(null);
+    });
+
+    it('Extract multiple valid JSONs (not supported)', () => {
+        const result = extractJsonPayload('Hey {"foo": "bar"} {"foo2": "bar2"}')
+        expect(result).toEqual(null);
+    });
+});