diff --git a/.README.md b/.README.md
index 548d488..a012ff4 100644
--- a/.README.md
+++ b/.README.md
@@ -422,6 +422,7 @@ Command|Description
 `cp <FROM> <TO>`|Copy files or dirs. Actually, it is an alias for `rsync -ahP`. Multiple `<FROM>` could be specified.
 `cp_merge <FROM> <TO>`|Mirror directories. Same as `rsync --delete`.
 `cp_link <FROM> <TO>`|Copy directory by recursively creating hardlinks and directories.
+`cp_test <FROM> <TO>`|Test cp_merge without writing anything.
 `bcp <FROM> <TO>`|Default `cp` command.
 
 ## Date.
diff --git a/.config/bash/module/cp.sh b/.config/bash/module/cp.sh
index 10c0c10..aaaf6ef 100644
--- a/.config/bash/module/cp.sh
+++ b/.config/bash/module/cp.sh
@@ -9,3 +9,6 @@ alias cp_link="/usr/bin/cp -lr"
 
 # default cp, a.k.a builtin cp.
 alias bcp="/usr/bin/cp"
+
+# cp_merge without writing anything.
+alias cp_test="rsync -ahP --chmod=u+w --delete -n"