TST: Avoid hard-coded port in test_webagg

QuLogic · QuLogic · commit 4890369effce · 2026-04-15T23:00:11.000-04:00
If the port's in use, then we want to allow retries and connect to
whichever port it ends up on.
diff --git a/lib/matplotlib/tests/test_backends_interactive.py b/lib/matplotlib/tests/test_backends_interactive.py
@@ -5,6 +5,7 @@
 import json
 import os
 import platform
+import re
 import signal
 import subprocess
 import sys
@@ -16,7 +17,6 @@
 
 import pytest
 
-import matplotlib as mpl
 from matplotlib import _c_internal_utils
 from matplotlib.backend_tools import ToolToggleBase
 from matplotlib.testing import subprocess_run_helper as _run_helper, is_ci_environment
@@ -46,7 +46,7 @@ def wait_for(self, terminator):
                     f'Subprocess died before emitting expected {terminator!r}')
             buf += c
             if buf.endswith(terminator):
-                return
+                return buf
 
 
 # Minimal smoke-testing of the backends for which the dependencies are
@@ -160,7 +160,6 @@ def _test_interactive_impl():
     from matplotlib.backend_bases import KeyEvent, FigureCanvasBase
     mpl.rcParams.update({
         "webagg.open_in_browser": False,
-        "webagg.port_retries": 1,
     })
 
     mpl.rcParams.update(json.loads(sys.argv[1]))
@@ -484,32 +483,33 @@ def test_cross_Qt_imports(host, mpl):
 @pytest.mark.skipif(sys.platform == "win32", reason="Cannot send SIGINT on Windows.")
 def test_webagg():
     pytest.importorskip("tornado")
-    proc = subprocess.Popen(
-        [sys.executable, "-c",
-         inspect.getsource(_test_interactive_impl)
-         + "\n_test_interactive_impl()", "{}"],
-        env={**os.environ, "MPLBACKEND": "webagg", "SOURCE_DATE_EPOCH": "0"})
-    url = f'http://{mpl.rcParams["webagg.address"]}:{mpl.rcParams["webagg.port"]}'
-    timeout = time.perf_counter() + _test_timeout
-    try:
-        while True:
-            try:
-                retcode = proc.poll()
-                # check that the subprocess for the server is not dead
-                assert retcode is None
-                conn = urllib.request.urlopen(url)
-                break
-            except urllib.error.URLError:
-                if time.perf_counter() > timeout:
-                    pytest.fail("Failed to connect to the webagg server.")
-                else:
-                    continue
-        conn.close()
-        proc.send_signal(signal.SIGINT)
-        assert proc.wait(timeout=_test_timeout) == 0
-    finally:
-        if proc.poll() is None:
-            proc.kill()
+    source = (inspect.getsource(_test_interactive_impl) +
+              "\n_test_interactive_impl()")
+    rc = '{"backend": "webagg"}'
+    with _WaitForStringPopen([sys.executable, "-c", source, rc]) as proc:
+        timeout = time.perf_counter() + _test_timeout
+        try:
+            buf = proc.wait_for('Press Ctrl+C')
+            url = re.search(r'visit (https?:\/\/\S+)', buf).group(1)
+            print(url)
+            while True:
+                try:
+                    retcode = proc.poll()
+                    # check that the subprocess for the server is not dead
+                    assert retcode is None
+                    conn = urllib.request.urlopen(url)
+                    break
+                except urllib.error.URLError:
+                    if time.perf_counter() > timeout:
+                        pytest.fail("Failed to connect to the webagg server.")
+                    else:
+                        continue
+            conn.close()
+            proc.send_signal(signal.SIGINT)
+            assert proc.wait(timeout=_test_timeout) == 0
+        finally:
+            if proc.poll() is None:
+                proc.kill()
 
 
 def _lazy_headless():
