feat: add unit tests for handler_hello and search_engine

tests/handler_hello_test.rs

@@ -0,0 +1,10 @@
+#[cfg(test)]
+mod tests {
+    use rustysearch::handler::hello::say_hello;
+    
+    #[tokio::test]
+    async fn test_say_hello() {
+        let result = say_hello().await;
+        assert_eq!(result, "Hello, World!");
+    }
+}

tests/search_engine_tests.rs

@@ -0,0 +1,14 @@
+#[cfg(test)]
+mod tests {
+    use rustysearch::search::engine::SearchEngine;
+
+    #[test]
+    fn test_search_engine() {
+        let mut search_engine = SearchEngine::new(1.2, 0.75);
+
+        search_engine.index("https://www.rust-lang.org/", "Rust Programming Language");
+
+        assert_eq!(search_engine.posts().len(), 1);
+        assert_eq!(search_engine.number_of_documents(), 1);
+    }
+}