Use fetch helper function instead of native

otherwise we cannot run the test on v16

supertest acts weird with the custom router, so we need to create a server manually

library/helpers/fetch.ts

@@ -52,16 +52,16 @@ async function request({
 
 export async function fetch({
   url,
-  method,
-  headers,
+  method = "GET",
+  headers = {},
   body = "",
-  timeoutInMS,
+  timeoutInMS = 5000,
 }: {
   url: URL;
-  method: string;
-  headers: Record<string, string>;
+  method?: string;
+  headers?: Record<string, string>;
   body?: string;
-  timeoutInMS: number;
+  timeoutInMS?: number;
 }): Promise<{ body: string; statusCode: number }> {
   const abort = new AbortController();
 

library/sources/Express.test.ts

@@ -5,6 +5,7 @@ import { Express } from "./Express";
 import { FileSystem } from "../sinks/FileSystem";
 import { HTTPServer } from "./HTTPServer";
 import { createTestAgent } from "../helpers/createTestAgent";
+import { fetch } from "../helpers/fetch";
 
 // Before require("express")
 const agent = createTestAgent({
@@ -639,8 +640,10 @@ t.test(
       throw new Error("address is a string");
     }
 
-    const response = await fetch(`http://localhost:${address!.port}/foo`);
-    t.same(await response.text(), "bar");
+    const response = await fetch({
+      url: new URL(`http://localhost:${address!.port}/foo`),
+    });
+    t.same(response.body, "bar");
     server.close();
 
     if (!routerLayer) {