Added Integration test template

tests/README.md

@@ -0,0 +1,8 @@
+# Integration test
+
+## Usage
+Here is a preview implementation of the integration test.
+
+```
+$ cargo test --test integration
+```

tests/integration.rs

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+use std::env;
+use std::path::PathBuf;
+use std::process::{Command, Stdio};
+
+#[test]
+fn main() {
+    let current_dir_path_result = env::current_dir();
+    let current_dir_path = match current_dir_path_result {
+        Ok(path_buf) => path_buf,
+        Err(_) => panic!("directory is not found"),
+    };
+    let youki_path = current_dir_path.join(PathBuf::from("youki"));
+    let status = Command::new(youki_path)
+        .stdout(Stdio::null())
+        .arg("-h")
+        .status()
+        .expect("failed to execute process");
+    assert!(status.success());
+}