chore: fix flaky netListenUnrefAndRef (#16892)

Closes #16890

cli/tests/unit/README.md

@@ -30,10 +30,10 @@ There are two ways to run `unit_test_runner.ts`:
 
 ```sh
 # Run all tests.
-target/debug/deno test --allow-all --unstable --location=http://js-unit-tests/foo/bar cli/tests/unit/
+cargo run --bin deno -- test --allow-all --unstable --location=http://js-unit-tests/foo/bar cli/tests/unit/
 
 # Run a specific test module
-target/debug/deno test --allow-all --unstable --location=http://js-unit-tests/foo/bar cli/tests/unit/files_test.ts
+cargo run --bin deno -- test --allow-all --unstable --location=http://js-unit-tests/foo/bar cli/tests/unit/files_test.ts
 ```
 
 ### Http server

cli/tests/unit/net_test.ts

@@ -8,6 +8,7 @@ import {
   deferred,
   delay,
   execCode,
+  execCode2,
 } from "./test_util.ts";
 import { join } from "../../../test_util/std/path/mod.ts";
 
@@ -853,25 +854,23 @@ Deno.test(
 Deno.test(
   { permissions: { read: true, run: true, net: true } },
   async function netListenUnrefAndRef() {
-    const p = execCode(`
+    const p = execCode2(`
       async function main() {
         const listener = Deno.listen({ port: 3500 });
         listener.unref();
         listener.ref(); // This restores 'ref' state of listener
+        console.log("started");
         await listener.accept();
         console.log("accepted")
       }
       main();
     `);
-    // TODO(kt3k): This is racy. Find a correct way to
-    // wait for the server to be ready
-    setTimeout(async () => {
-      const conn = await Deno.connect({ port: 3500 });
-      conn.close();
-    }, 200);
-    const [statusCode, output] = await p;
+    await p.waitStdoutText("started");
+    const conn = await Deno.connect({ port: 3500 });
+    conn.close();
+    const [statusCode, output] = await p.finished();
     assertEquals(statusCode, 0);
-    assertEquals(output.trim(), "accepted");
+    assertEquals(output.trim(), "started\naccepted");
   },
 );
 

cli/tests/unit/test_util.ts

@@ -29,16 +29,53 @@ export function pathToAbsoluteFileUrl(path: string): URL {
   return new URL(`file://${Deno.build.os === "windows" ? "/" : ""}${path}`);
 }
 
-const decoder = new TextDecoder();
+export function execCode(code: string): Promise<readonly [number, string]> {
+  return execCode2(code).finished();
+}
 
-export async function execCode(code: string): Promise<[number, string]> {
-  const output = await new Deno.Command(Deno.execPath(), {
+export function execCode2(code: string) {
+  const command = new Deno.Command(Deno.execPath(), {
     args: [
       "eval",
       "--unstable",
       "--no-check",
       code,
     ],
-  }).output();
-  return [output.code, decoder.decode(output.stdout)];
+    stdout: "piped",
+    stderr: "inherit",
+  });
+
+  const child = command.spawn();
+  const stdout = child.stdout.pipeThrough(new TextDecoderStream()).getReader();
+  let output = "";
+
+  return {
+    async waitStdoutText(text: string) {
+      while (true) {
+        const readData = await stdout.read();
+        if (readData.value) {
+          output += readData.value;
+          if (output.includes(text)) {
+            return;
+          }
+        }
+        if (readData.done) {
+          throw new Error(`Did not find text '${text}' in stdout.`);
+        }
+      }
+    },
+    async finished() {
+      while (true) {
+        const readData = await stdout.read();
+        if (readData.value) {
+          output += readData.value;
+        }
+        if (readData.done) {
+          break;
+        }
+      }
+      const status = await child.status;
+      return [status.code, output] as const;
+    },
+  };
 }