diff --git a/src/testdir/unix.vim b/src/testdir/unix.vim
new file mode 100644
index 0000000..f766e74
--- /dev/null
+++ b/src/testdir/unix.vim
@@ -0,0 +1,3 @@
+" Settings for test script execution
+" Always use "sh", don't use the value of "$SHELL".
+set shell=sh