Feat: Add test case for find_matches

Slight find_matches rewrite to use Write trait.

src/main.rs

@@ -19,21 +19,29 @@ fn main() -> Result<()> {
     let content = std::fs::read_to_string(&args.path)
         .with_context(|| format!("could not read file `{}`.", args.path.display()))?;
 
-
-    find_matches(content.as_str(), args.pattern.as_str());
+    find_matches(
+        content.as_str(),
+        args.pattern.as_str(),
+        &mut std::io::stdout(),
+    );
 
     Ok(())
 }
 
-fn find_matches(content: &str, pattern: &str) {
+fn find_matches(content: &str, pattern: &str, mut writer: impl std::io::Write) {
     for line in content.lines() {
         if line.contains(pattern) {
-            println!("{}", line)
+            writeln!(writer, "{}", line);
         }
     }
 }
 
-
+#[test]
+fn find_a_match() {
+    let mut result = Vec::new();
+    find_matches("lorem ipsum\ndolar sit amet", "lorem", &mut result);
+    assert_eq!(result, b"lorem ipsum\n")
+}
 
 #[allow(dead_code)]
 fn answer() -> i32 {