Add objectToQueryString utility function and it's unit tests

test/objectToQueryString.test.js

@@ -0,0 +1,29 @@
+const {objectToQueryString} = require('./_30s.js');
+
+test('objectToQueryString is a Function', () => {
+  expect(objectToQueryString).toBeInstanceOf(Function);
+});
+
+test("{page: '1', size: '2kg', key: '21'} to give '?page=1&size=2kg&key=21'", () => {
+  expect(
+    objectToQueryString({page: '1', size: '2kg', key: '21'})
+  ).toEqual('?page=1&size=2kg&key=21');
+});
+
+test("{page: '1', size: '2kg', key: undefined} to give '?page=1&size=2kg'", () => {
+  expect(
+    objectToQueryString({page: '1', size: '2kg', key: undefined})
+  ).toEqual('?page=1&size=2kg');
+});
+
+test("{} to give ''", () => {
+  expect(
+    objectToQueryString({})
+  ).toEqual('');
+});
+
+test("{page: 1, size: null, key: undefined} to give ''", () => {
+  expect(
+    objectToQueryString({page: 1, size: null, key: undefined})
+  ).toEqual('');
+});