+test_expect_success 'verify resulting packs' '
+       git verify-pack test-11-*.pack
+'
+
+#
+# WARNING!
+#
+# The following test is destructive.  Please keep the next
+# two tests at the end of this file.
+#
+
+test_expect_success \
+    'fake a SHA1 hash collision' \
+    'test -f   .git/objects/c8/2de19312b6c3695c0c18f70709a6c535682a67 &&
+     cp -f     .git/objects/9d/235ed07cd19811a6ceb342de82f190e49c9f68 \
+               .git/objects/c8/2de19312b6c3695c0c18f70709a6c535682a67'
+
+test_expect_success \
+    'make sure index-pack detects the SHA1 collision' \
+    'test_must_fail git index-pack -o bad.idx test-3.pack 2>msg &&
+     grep "SHA1 COLLISION FOUND" msg'
+