Add some simple tests for joinUrls behavior

src/fetchBaseQuery.ts

@@ -32,7 +32,9 @@ export function fetchBaseQuery({ baseUrl }: { baseUrl?: string } = {}) {
       body,
       ...rest,
     };
+
     config.headers = new Headers(headers);
+
     if (!config.headers.has('content-type')) {
       config.headers.set('content-type', 'application/json');
     }
@@ -42,10 +44,12 @@ export function fetchBaseQuery({ baseUrl }: { baseUrl?: string } = {}) {
     }
 
     url = joinUrls(baseUrl, url);
+
     if (params) {
       const searchParams = new URLSearchParams(params);
       url += `?${searchParams.toString()}`;
     }
+
     const response = await fetch(url, config);
 
     let resultData;

src/utils/joinsUrls.test.ts

@@ -0,0 +1,28 @@
+import { joinUrls } from './joinUrls';
+
+test('correctly joins variations relative urls', () => {
+  expect(joinUrls('/api/', '/banana')).toBe('/api/banana');
+  expect(joinUrls('/api', '/banana')).toBe('/api/banana');
+
+  expect(joinUrls('/api/', 'banana')).toBe('/api/banana');
+  expect(joinUrls('/api/', '/banana/')).toBe('/api/banana/');
+
+  expect(joinUrls('/', '/banana/')).toBe('/banana/');
+  expect(joinUrls('/', 'banana/')).toBe('/banana/');
+
+  expect(joinUrls('/', '/banana')).toBe('/banana');
+  expect(joinUrls('/', 'banana')).toBe('/banana');
+
+  expect(joinUrls('', '/banana')).toBe('/banana');
+  expect(joinUrls('', 'banana')).toBe('banana');
+});
+
+test('correctly joins variations of absolute urls', () => {
+  expect(joinUrls('https://apple.com', '/api/banana/')).toBe('https://apple.com/api/banana/');
+  expect(joinUrls('https://apple.com', '/api/banana')).toBe('https://apple.com/api/banana');
+
+  expect(joinUrls('https://apple.com/', 'api/banana/')).toBe('https://apple.com/api/banana/');
+  expect(joinUrls('https://apple.com/', 'api/banana')).toBe('https://apple.com/api/banana');
+
+  expect(joinUrls('https://apple.com/', 'api/banana/')).toBe('https://apple.com/api/banana/');
+});