Issue #12141: Install copies of template C module file so that

test_build_ext of test_distutils and test_command_build_ext of
test_packaging are no longer silently skipped when
run outside of a build directory.

Lib/distutils/tests/test_build_ext.py

@@ -22,6 +22,11 @@ from test.support import run_unittest
 ALREADY_TESTED = False
 
 def _get_source_filename():
+    # use installed copy if available
+    tests_f = os.path.join(os.path.dirname(__file__), 'xxmodule.c')
+    if os.path.exists(tests_f):
+        return tests_f
+    # otherwise try using copy from build directory
     srcdir = sysconfig.get_config_var('srcdir')
     return os.path.join(srcdir, 'Modules', 'xxmodule.c')
 

Lib/packaging/tests/test_command_build_ext.py

@@ -14,6 +14,11 @@ from packaging.tests import support, unittest, verbose, unload
 
 
 def _get_source_filename():
+    # use installed copy if available
+    tests_f = os.path.join(os.path.dirname(__file__), 'xxmodule.c')
+    if os.path.exists(tests_f):
+        return tests_f
+    # otherwise try using copy from build directory
     srcdir = sysconfig.get_config_var('srcdir')
     return os.path.join(srcdir, 'Modules', 'xxmodule.c')
 

Makefile.pre.in

@@ -982,7 +982,7 @@ LIBSUBDIRS=	tkinter tkinter/test tkinter/test/test_tkinter \
 		multiprocessing multiprocessing/dummy \
 		unittest unittest/test \
 		curses pydoc_data $(MACHDEPS)
-libinstall:	build_all $(srcdir)/Lib/$(PLATDIR)
+libinstall:	build_all $(srcdir)/Lib/$(PLATDIR) $(srcdir)/Modules/xxmodule.c
 	@for i in $(SCRIPTDIR) $(LIBDEST); \
 	do \
 		if test ! -d $(DESTDIR)$$i; then \
@@ -1038,6 +1038,14 @@ libinstall:	build_all $(srcdir)/Lib/$(PLATDIR)
 		done; \
 	done
 	$(INSTALL_DATA) $(srcdir)/LICENSE $(DESTDIR)$(LIBDEST)/LICENSE.txt
+	if test -d $(DESTDIR)$(LIBDEST)/distutils/tests; then \
+		$(INSTALL_DATA) $(srcdir)/Modules/xxmodule.c \
+			$(DESTDIR)$(LIBDEST)/distutils/tests ; \
+	fi
+	if test -d $(DESTDIR)$(LIBDEST)/packaging/tests; then \
+		$(INSTALL_DATA) $(srcdir)/Modules/xxmodule.c \
+			$(DESTDIR)$(LIBDEST)/packaging/tests ; \
+	fi
 	-PYTHONPATH=$(DESTDIR)$(LIBDEST)  $(RUNSHARED) \
 		./$(BUILDPYTHON) -Wi $(DESTDIR)$(LIBDEST)/compileall.py \
 		-d $(LIBDEST) -f \

Misc/NEWS

@@ -913,6 +913,11 @@ Extension Modules
 Tests
 -----
 
+- Issue #12141: Install copies of template C module file so that
+  test_build_ext of test_distutils and test_command_build_ext of
+  test_packaging are no longer silently skipped when
+  run outside of a build directory.
+
 - Issue #8746: Add additional tests for os.chflags() and os.lchflags().
   Patch by Garrett Cooper.