bpo-40723: Make IDLE autocomplete test run without __main__.__file__ (GH-20311)

This was the only failure running unittest.main(test.test_idle) after imports.
(cherry picked from commit 905b3cd)

Co-authored-by: Florian Dahlitz <[email protected]>

Author: miss-islington

Lib/idlelib/NEWS.txt

@@ -3,6 +3,8 @@ Released on 2020-10-05?
 ======================================
 
 
+bpo-40723: Make test_idle pass when run after import.
+
 bpo-38689: IDLE will no longer freeze when inspect.signature fails
 when fetching a calltip.
 

Lib/idlelib/idle_test/test_autocomplete.py

@@ -227,7 +227,7 @@ def test_fetch_completions(self):
         acp = self.autocomplete
         small, large = acp.fetch_completions(
                 '', ac.ATTRS)
-        if __main__.__file__ != ac.__file__:
+        if hasattr(__main__, '__file__') and __main__.__file__ != ac.__file__:
             self.assertNotIn('AutoComplete', small)  # See issue 36405.
 
         # Test attributes

Misc/NEWS.d/next/IDLE/2020-05-24-06-19-43.bpo-40723.AJLd4U.rst

@@ -0,0 +1 @@
+Make test_idle pass when run after import.