Add a few simple integration tests

tests/helpers.rs

@@ -0,0 +1,11 @@
+use tempdir::TempDir;
+
+pub fn init_tmpdir() -> TempDir {
+    let tmp_dir = TempDir::new("grm-test").unwrap();
+    println!("Temporary directory: {}", tmp_dir.path().display());
+    tmp_dir
+}
+
+pub fn cleanup_tmpdir(tempdir: TempDir) {
+    tempdir.close().unwrap();
+}