Use sys.executable to run Python, as suggested by Neal Norwitz.
diff --git a/Lib/test/test_atexit.py b/Lib/test/test_atexit.py
index ad5bced..64c4c3c 100644
--- a/Lib/test/test_atexit.py
+++ b/Lib/test/test_atexit.py
@@ -2,6 +2,7 @@
from test_support import TESTFN, vereq
import atexit
import os
+import sys
input = """\
import atexit
@@ -22,7 +23,7 @@
f.write(input)
f.close()
-p = os.popen("python " + fname)
+p = os.popen("%s %s" % (sys.executable, fname))
output = p.read()
p.close()
vereq(output, """\
@@ -50,7 +51,7 @@
f.write(input)
f.close()
-p = os.popen("python " + fname)
+p = os.popen("%s %s" % (sys.executable, fname))
output = p.read()
p.close()
vereq(output, """\