test: deflake test-http2-debug

Native debug writes can be lost when the non-blocking stderr pipe fills,
leaving expected log lines missing even when the child exits
successfully. Capture stderr in a temporary file and apply the existing
assertions to its contents. Remove the flaky designation on Linux s390x.

Fixes: #58353
Signed-off-by: Filip Skokan <panva.ip@gmail.com>
Assisted-by: Codex

Author: panva

test/parallel/parallel.status

@@ -35,10 +35,6 @@ test-performance-function: PASS, FLAKY
 # https://github.com/nodejs/node/issues/54346
 test-esm-loader-hooks-inspect-wait: PASS, FLAKY
 
-[$system==linux && $arch==s390x]
-# https://github.com/nodejs/node/issues/58353
-test-http2-debug: PASS, FLAKY
-
 [$system==macos]
 # https://github.com/nodejs/node/issues/42741
 test-http-server-headers-timeout-keepalive: PASS,FLAKY

test/parallel/test-http2-debug.js

@@ -5,27 +5,37 @@ if (!common.hasCrypto)
   common.skip('missing crypto');
 const assert = require('assert');
 const { spawnSyncAndAssert } = require('../common/child_process');
+const fs = require('fs');
 const path = require('path');
+const tmpdir = require('../common/tmpdir');
 
-spawnSyncAndAssert(process.execPath, [
-  path.resolve(__dirname, 'test-http2-ping.js'),
-], {
-  env: {
-    ...process.env,
-    NODE_DEBUG: 'http2',
-    NODE_DEBUG_NATIVE: 'http2',
-  },
-}, {
-  trim: true,
-  stderr(output) {
-    assert.match(output,
-                 /Setting the NODE_DEBUG environment variable to 'http2' can expose sensitive data/);
-    assert.match(output, /\(such as passwords, tokens and authentication headers\) in the resulting log\.\r?\n/);
-    assert.match(output, /Http2Session client \(\d+\) handling data frame for stream \d+\r?\n/);
-    assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session client \(\d+\)\] reading starting\r?\n/);
-    assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session client \(\d+\)\] closed with code 0\r?\n/);
-    assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session server \(\d+\)\] closed with code 0\r?\n/);
-    assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session server \(\d+\)\] tearing down stream\r?\n/);
-  },
-  stdout: ''
-});
+tmpdir.refresh();
+const stderrFile = tmpdir.resolve('stderr.log');
+// Native debug writes can be lost when a non-blocking stderr pipe fills.
+const stderrFd = fs.openSync(stderrFile, 'w');
+try {
+  spawnSyncAndAssert(process.execPath, [
+    path.resolve(__dirname, 'test-http2-ping.js'),
+  ], {
+    env: {
+      ...process.env,
+      NODE_DEBUG: 'http2',
+      NODE_DEBUG_NATIVE: 'http2',
+    },
+    stdio: ['pipe', 'pipe', stderrFd],
+  }, {
+    stdout: ''
+  });
+} finally {
+  fs.closeSync(stderrFd);
+}
+
+const output = fs.readFileSync(stderrFile, 'utf8');
+assert.match(output,
+             /Setting the NODE_DEBUG environment variable to 'http2' can expose sensitive data/);
+assert.match(output, /\(such as passwords, tokens and authentication headers\) in the resulting log\.\r?\n/);
+assert.match(output, /Http2Session client \(\d+\) handling data frame for stream \d+\r?\n/);
+assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session client \(\d+\)\] reading starting\r?\n/);
+assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session client \(\d+\)\] closed with code 0\r?\n/);
+assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session server \(\d+\)\] closed with code 0\r?\n/);
+assert.match(output, /HttpStream \d+ \(\d+\) \[Http2Session server \(\d+\)\] tearing down stream\r?\n/);