Feat: Add test case covering empty string.

tests/cli.rs

@@ -28,3 +28,18 @@ fn find_content_in_file() -> Result<(), Box<dyn std::error::Error>> {
 
     Ok(())
 }
+
+#[test]
+fn find_empty_string() -> Result<(), Box<dyn std::error::Error>> {
+    let file = assert_fs::NamedTempFile::new("sample.txt")?;
+    let content = "A test\nActual content\nMore content\nAnother test";
+    file.write_str(content)?;
+
+    let mut cmd = Command::cargo_bin("grrs")?;
+    cmd.arg("").arg(file.path());
+    cmd.assert()
+        .success()
+        .stdout(predicate::str::contains(content));
+
+    Ok(())
+}