+test_description='git am with corrupt input'
+# Note the missing "+++" line:
+cat > bad-patch.diff <<'EOF'
+From: A U Thor <email@example.com>
+index 7898192..6178079 100644
+test_expect_success setup '
+# This used to fail before, too, but with a different diagnostic.
+# fatal: unable to write file '(null)' mode 100644: Bad address
+# Also, it had the unwanted side-effect of deleting f.
+test_expect_success 'try to apply corrupted patch' '
+ git am bad-patch.diff 2> actual
+fatal: git diff header lacks filename information (line 4)
+test_expect_success 'compare diagnostic; ensure file is still here' '
+ test_cmp expected actual