Add watch run unit test

cli-bin/Cargo.toml

@@ -22,12 +22,15 @@ tracing            = "0.1"
 tracing-subscriber = { version = "0.3", features = ["fmt", "env-filter"] }
 walkdir            = "2.5"
 serde_json         = { version = "1", optional = true }
+once_cell          = "1"
 
 [dev-dependencies]
 assert_cmd = "2"
 predicates  = "3"
 tempfile    = "3"
 dirs        = "5"
+once_cell   = "1"
+libc        = "0.2"
 
 [features]
 # Enable JSON output with `--features json`