Fix 13314 add all plugins to pytester subprocess

AUTHORS

@@ -345,6 +345,7 @@ Pavel Karateev
 Pavel Zhukov
 Paweł Adamczak
 Pedro Algarvio
+Peter Kovary
 Petter Strandmark
 Philipp Loose
 Pierre Sassoulas

changelog/13314.bugfix.rst

@@ -0,0 +1 @@
+Fix bug where ``pytester.runpytest_subprocess`` only included the first plugin from ``pytester.plugins``. Now it correctly includes all of them.

src/_pytest/pytester.py

@@ -1485,13 +1485,15 @@ def runpytest_subprocess(
             The result.
         """
         __tracebackhide__ = True
+        pytest_args = list(self._getpytestargs())
+        for plugin in self.plugins:
+            if isinstance(plugin, str):
+                pytest_args += ["-p", plugin]
+
         p = make_numbered_dir(root=self.path, prefix="runpytest-", mode=0o700)
-        args = (f"--basetemp={p}", *args)
-        plugins = [x for x in self.plugins if isinstance(x, str)]
-        if plugins:
-            args = ("-p", plugins[0], *args)
-        args = self._getpytestargs() + args
-        return self.run(*args, timeout=timeout)
+        pytest_args.append(f"--basetemp={p}")
+
+        return self.run(*pytest_args, *args, timeout=timeout)
 
     def spawn_pytest(self, string: str, expect_timeout: float = 10.0) -> pexpect.spawn:
         """Run pytest using pexpect.

testing/test_pytester.py

@@ -472,6 +472,20 @@ def test_timeout():
         pytester.runpytest_subprocess(testfile, timeout=1)
 
 
+def test_pytester_subprocess_with_plugins(pytester: Pytester) -> None:
+    testfile = pytester.makepyfile(
+        """
+        def test_plugins(pytestconfig):
+            plugins = pytestconfig.pluginmanager.list_name_plugin()
+            assert ("plug_1", None) in plugins
+            assert ("plug_2", None) in plugins
+        """
+    )
+    pytester.plugins.extend(["no:plug_1", "no:plug_2"])
+
+    pytester.runpytest_subprocess(testfile).assert_outcomes(passed=1)
+
+
 def test_linematcher_with_nonlist() -> None:
     """Test LineMatcher with regard to passing in a set (accidentally)."""
     from _pytest._code.source import Source