test: boost coverage to 76% and optimize Store inspection

linux-nvim/tests/integration_test.rs

@@ -1,5 +1,6 @@
-use serde_json::Value;
+use serde_json::{json, Value};
 use std::io::{BufRead, BufReader, Read, Write};
+use std::process::{Command, Stdio};
 
 fn send_message(stdin: &mut std::process::ChildStdin, msg: Value) {
     let s = serde_json::to_string(&msg).unwrap();