test: added more tests (#16)

Co-authored-by: Sharang Parnerkar <parnerkarsharang@gmail.com>
Reviewed-on: #16

src/models/news.rs

@@ -23,3 +23,61 @@ pub struct NewsCard {
     pub thumbnail_url: Option<String>,
     pub published_at: String,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn news_card_serde_round_trip() {
+        let card = NewsCard {
+            title: "AI Breakthrough".into(),
+            source: "techcrunch.com".into(),
+            summary: "New model released".into(),
+            content: "Full article content here".into(),
+            category: "AI".into(),
+            url: "https://example.com/article".into(),
+            thumbnail_url: Some("https://example.com/thumb.jpg".into()),
+            published_at: "2025-06-01".into(),
+        };
+        let json = serde_json::to_string(&card).expect("serialize NewsCard");
+        let back: NewsCard = serde_json::from_str(&json).expect("deserialize NewsCard");
+        assert_eq!(card, back);
+    }
+
+    #[test]
+    fn news_card_thumbnail_none() {
+        let card = NewsCard {
+            title: "No Thumb".into(),
+            source: "bbc.com".into(),
+            summary: "Summary".into(),
+            content: "Content".into(),
+            category: "Tech".into(),
+            url: "https://bbc.com/article".into(),
+            thumbnail_url: None,
+            published_at: "2025-06-01".into(),
+        };
+        let json = serde_json::to_string(&card).expect("serialize");
+        let back: NewsCard = serde_json::from_str(&json).expect("deserialize");
+        assert_eq!(card, back);
+    }
+
+    #[test]
+    fn news_card_thumbnail_some() {
+        let card = NewsCard {
+            title: "With Thumb".into(),
+            source: "cnn.com".into(),
+            summary: "Summary".into(),
+            content: "Content".into(),
+            category: "News".into(),
+            url: "https://cnn.com/article".into(),
+            thumbnail_url: Some("https://cnn.com/img.jpg".into()),
+            published_at: "2025-06-01".into(),
+        };
+        let json = serde_json::to_string(&card).expect("serialize");
+        assert!(json.contains("img.jpg"));
+        let back: NewsCard = serde_json::from_str(&json).expect("deserialize");
+        assert_eq!(card.thumbnail_url, back.thumbnail_url);
+    }
+}