tests/import/import_pkg9.py: Add test for subpackage attribute.

When foo.bar is imported, bar is added as an attribute to foo. Previously
this happened on every import, but should only happen on first import.

This verifies the behavior for relative imports and overriding.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

tests/import/import_pkg9.py

@@ -0,0 +1,16 @@
+# tests that import only sets subpackage attribute on first import
+
+import pkg9
+
+pkg9.mod1()
+pkg9.mod2()
+
+import pkg9.mod1
+
+pkg9.mod1()
+pkg9.mod2()
+
+import pkg9.mod2
+
+pkg9.mod1()
+print(pkg9.mod2.__name__, type(pkg9.mod2).__name__)

tests/import/pkg9/__init__.py

@@ -0,0 +1,5 @@
+from .mod1 import mod1
+
+
+def mod2():
+    print("mod2")

tests/import/pkg9/mod1.py

@@ -0,0 +1,2 @@
+def mod1():
+    print("mod1")

tests/import/pkg9/mod2.py

@@ -0,0 +1 @@
+from . import mod2