diff --git a/Cargo.toml b/Cargo.toml
index 74515aa..486db13 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,3 +16,7 @@ futures-util = "0.3"
 async-channel = "2.3"
 pulldown-cmark = { version = "0.13.0", default-features = false, features = ["html"] }
 thiserror = "2"
+
+[dev-dependencies]
+mockito = "1"
+tempfile = "3"
diff --git a/src/api.rs b/src/api.rs
index 4e40901..5188e91 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -132,4 +132,191 @@ pub async fn send_chat_request_streaming(
     }
 
     Ok(full_response)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // ── fetch_models ─────────────────────────────────────────────────────────
+
+    #[tokio::test]
+    async fn fetch_models_returns_model_list() {
+        let mut server = mockito::Server::new_async().await;
+        let _mock = server
+            .mock("GET", "/api/tags")
+            .with_status(200)
+            .with_header("content-type", "application/json")
+            .with_body(r#"{"models":[{"name":"llama3","modified_at":"2024-01-01T00:00:00Z","size":4000000}]}"#)
+            .create_async()
+            .await;
+
+        let models = fetch_models(&server.url()).await.unwrap();
+        assert_eq!(models.len(), 1);
+        assert_eq!(models[0].name, "llama3");
+    }
+
+    #[tokio::test]
+    async fn fetch_models_bad_status_returns_error() {
+        let mut server = mockito::Server::new_async().await;
+        let _mock = server
+            .mock("GET", "/api/tags")
+            .with_status(500)
+            .create_async()
+            .await;
+
+        let err = fetch_models(&server.url()).await.unwrap_err();
+        // reqwest treats non-success as an error only if we explicitly check;
+        // here fetch_models passes the status through response.json() which will
+        // fail because body is empty — so we get an Http or Parse error.
+        // The important thing: it is an error, not a success.
+        assert!(matches!(err, ApiError::Http(_) | ApiError::Parse(_) | ApiError::BadStatus(_)));
+    }
+
+    #[tokio::test]
+    async fn fetch_models_bad_json_returns_parse_error() {
+        let mut server = mockito::Server::new_async().await;
+        let _mock = server
+            .mock("GET", "/api/tags")
+            .with_status(200)
+            .with_header("content-type", "application/json")
+            .with_body("not json")
+            .create_async()
+            .await;
+
+        let err = fetch_models(&server.url()).await.unwrap_err();
+        assert!(matches!(err, ApiError::Http(_) | ApiError::Parse(_)));
+    }
+
+    // ── send_chat_request_streaming ──────────────────────────────────────────
+
+    fn ndjson_lines(tokens: &[(&str, bool)]) -> String {
+        tokens
+            .iter()
+            .map(|(content, done)| {
+                format!(
+                    r#"{{"model":"llama3","created_at":"2024-01-01T00:00:00Z","message":{{"role":"assistant","content":"{}"}},"done":{}}}"#,
+                    content, done
+                )
+            })
+            .collect::<Vec<_>>()
+            .join("\n")
+    }
+
+    async fn run_streaming(server_url: &str, batch_size: usize) -> (Result<String, ApiError>, Vec<String>) {
+        let messages = vec![ChatMessage {
+            role: "user".to_string(),
+            content: "hi".to_string(),
+        }];
+        let (tx, rx) = async_channel::unbounded();
+        let result = send_chat_request_streaming(
+            server_url, "llama3", messages, tx, batch_size, 5000,
+        )
+        .await;
+
+        let mut batches = Vec::new();
+        while let Ok(batch) = rx.try_recv() {
+            batches.push(batch);
+        }
+        (result, batches)
+    }
+
+    #[tokio::test]
+    async fn streaming_single_token_returns_full_response() {
+        let mut server = mockito::Server::new_async().await;
+        let body = ndjson_lines(&[("Hello", true)]);
+        let _mock = server
+            .mock("POST", "/api/chat")
+            .with_status(200)
+            .with_body(body)
+            .create_async()
+            .await;
+
+        let (result, _batches) = run_streaming(&server.url(), 100).await;
+        assert_eq!(result.unwrap(), "Hello");
+    }
+
+    #[tokio::test]
+    async fn streaming_multi_token_accumulates_full_response() {
+        let mut server = mockito::Server::new_async().await;
+        let body = ndjson_lines(&[("Hello", false), (" world", true)]);
+        let _mock = server
+            .mock("POST", "/api/chat")
+            .with_status(200)
+            .with_body(body)
+            .create_async()
+            .await;
+
+        let (result, _) = run_streaming(&server.url(), 100).await;
+        assert_eq!(result.unwrap(), "Hello world");
+    }
+
+    #[tokio::test]
+    async fn streaming_batch_size_flushes_intermediate_batches() {
+        let mut server = mockito::Server::new_async().await;
+        // 3 tokens, batch_size=2 → first batch sent after 2 tokens, second after done
+        let body = ndjson_lines(&[("a", false), ("b", false), ("c", true)]);
+        let _mock = server
+            .mock("POST", "/api/chat")
+            .with_status(200)
+            .with_body(body)
+            .create_async()
+            .await;
+
+        let (result, batches) = run_streaming(&server.url(), 2).await;
+        assert_eq!(result.unwrap(), "abc");
+        // We should have received at least 2 channel messages (one mid-stream, one final)
+        assert!(batches.len() >= 2, "expected intermediate batches, got {:?}", batches);
+        assert_eq!(batches.join(""), "abc");
+    }
+
+    #[tokio::test]
+    async fn streaming_done_with_no_content_returns_empty_response_error() {
+        let mut server = mockito::Server::new_async().await;
+        // done:true but content is empty
+        let body = r#"{"model":"llama3","created_at":"2024-01-01T00:00:00Z","message":{"role":"assistant","content":""},"done":true}"#;
+        let _mock = server
+            .mock("POST", "/api/chat")
+            .with_status(200)
+            .with_body(body)
+            .create_async()
+            .await;
+
+        let (result, _) = run_streaming(&server.url(), 100).await;
+        assert!(matches!(result, Err(ApiError::EmptyResponse)));
+    }
+
+    #[tokio::test]
+    async fn streaming_bad_status_returns_error() {
+        let mut server = mockito::Server::new_async().await;
+        let _mock = server
+            .mock("POST", "/api/chat")
+            .with_status(503)
+            .create_async()
+            .await;
+
+        let (result, _) = run_streaming(&server.url(), 100).await;
+        assert!(matches!(result, Err(ApiError::BadStatus(503))));
+    }
+
+    #[tokio::test]
+    async fn streaming_malformed_json_line_is_skipped() {
+        let mut server = mockito::Server::new_async().await;
+        // A bad line in the middle should not abort processing
+        let body = format!(
+            "{}\nnot valid json\n{}",
+            r#"{"model":"llama3","created_at":"2024-01-01T00:00:00Z","message":{"role":"assistant","content":"Hello"},"done":false}"#,
+            r#"{"model":"llama3","created_at":"2024-01-01T00:00:00Z","message":{"role":"assistant","content":" world"},"done":true}"#,
+        );
+        let _mock = server
+            .mock("POST", "/api/chat")
+            .with_status(200)
+            .with_body(body)
+            .create_async()
+            .await;
+
+        let (result, _) = run_streaming(&server.url(), 100).await;
+        // Should still accumulate valid tokens despite the bad line
+        assert_eq!(result.unwrap(), "Hello world");
+    }
 }
\ No newline at end of file
diff --git a/src/config.rs b/src/config.rs
index 1a8656d..f58a1cf 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -155,4 +155,62 @@ impl Config {
         
         Ok(config_dir.join("config.toml"))
     }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_config_has_sensible_values() {
+        let cfg = Config::default();
+
+        // Ollama endpoint
+        assert_eq!(cfg.ollama.url, "http://localhost:11434");
+        assert!(cfg.ollama.timeout_seconds > 0);
+
+        // Context window: 0 would mean every request sends zero messages — bad default.
+        assert!(cfg.ollama.max_context_messages > 0,
+            "max_context_messages must be > 0 or no history is ever sent");
+
+        // Streaming
+        assert!(cfg.streaming.batch_size > 0);
+        assert!(cfg.streaming.batch_timeout_ms > 0);
+
+        // System prompt empty by default (RAG / user sets it when needed)
+        assert!(cfg.ollama.system_prompt.is_empty());
+    }
+
+    #[test]
+    fn config_roundtrips_through_toml() {
+        // Serialize to TOML and back — verifies the serde field names are stable.
+        // If you rename a field in the struct but forget to update the serde attribute,
+        // existing config files on disk will silently lose that value. This catches it.
+        let original = Config::default();
+        let toml_str = toml::to_string_pretty(&original).unwrap();
+        let parsed: Config = toml::from_str(&toml_str).unwrap();
+
+        assert_eq!(parsed.ollama.url, original.ollama.url);
+        assert_eq!(parsed.ollama.max_context_messages, original.ollama.max_context_messages);
+        assert_eq!(parsed.streaming.batch_size, original.streaming.batch_size);
+        assert_eq!(parsed.streaming.batch_timeout_ms, original.streaming.batch_timeout_ms);
+        assert_eq!(parsed.ui.window_font_size, original.ui.window_font_size);
+    }
+
+    #[test]
+    fn config_roundtrip_preserves_custom_values() {
+        let mut cfg = Config::default();
+        cfg.ollama.url = "http://my-server:11434".to_string();
+        cfg.ollama.max_context_messages = 50;
+        cfg.streaming.batch_size = 5;
+        cfg.ollama.system_prompt = "You are a helpful assistant.".to_string();
+
+        let toml_str = toml::to_string_pretty(&cfg).unwrap();
+        let parsed: Config = toml::from_str(&toml_str).unwrap();
+
+        assert_eq!(parsed.ollama.url, "http://my-server:11434");
+        assert_eq!(parsed.ollama.max_context_messages, 50);
+        assert_eq!(parsed.streaming.batch_size, 5);
+        assert_eq!(parsed.ollama.system_prompt, "You are a helpful assistant.");
+    }
 }
\ No newline at end of file
diff --git a/src/markdown_renderer.rs b/src/markdown_renderer.rs
index e252cd3..fd504ee 100644
--- a/src/markdown_renderer.rs
+++ b/src/markdown_renderer.rs
@@ -181,56 +181,19 @@ impl MarkdownRenderer {
         }
     }
     
-    /// Process text for streaming, handling think tags in real-time
+    /// Process text for streaming, handling think tags in real-time.
+    ///
+    /// Delegates detection to [`parse_think_segments`] and handles GTK insertions per segment.
     fn process_streaming_text(&mut self, buffer: &TextBuffer, text: &str, iter: &mut TextIter) -> String {
         let mut result = String::new();
-        let mut remaining = text;
-        
-        while !remaining.is_empty() {
-            if self.in_think_tag {
-                // We're currently inside a think tag, look for closing tag
-                if let Some(end_pos) = remaining.find("</think>") {
-                    // Found closing tag - stream the remaining think content
-                    let final_think_content = &remaining[..end_pos];
-                    if !final_think_content.is_empty() {
-                        buffer.insert_with_tags(iter, final_think_content, &[&self.think_tag]);
-                    }
-                    
-                    // Close the think section
-                    buffer.insert(iter, "\n\n");
-                    
-                    // Reset think state
-                    self.in_think_tag = false;
-                    
-                    // Continue with text after closing tag
-                    remaining = &remaining[end_pos + 8..]; // 8 = "</think>".len()
-                } else {
-                    // No closing tag yet, stream the think content as it arrives
-                    if !remaining.is_empty() {
-                        buffer.insert_with_tags(iter, remaining, &[&self.think_tag]);
-                    }
-                    break; // Wait for more streaming content
-                }
-            } else {
-                // Not in think tag, look for opening tag
-                if let Some(start_pos) = remaining.find("<think>") {
-                    // Add content before think tag to result for normal processing
-                    result.push_str(&remaining[..start_pos]);
-                    
-                    // Start think mode and show the think indicator
-                    self.in_think_tag = true;
-                    buffer.insert(iter, "\n💭 ");
-                    
-                    // Continue with content after opening tag
-                    remaining = &remaining[start_pos + 7..]; // 7 = "<think>".len()
-                } else {
-                    // No think tag found, add all remaining text to result
-                    result.push_str(remaining);
-                    break;
-                }
+        for segment in parse_think_segments(text, &mut self.in_think_tag) {
+            match segment {
+                StreamSegment::Normal(s) => result.push_str(&s),
+                StreamSegment::ThinkStart => buffer.insert(iter, "\n💭 "),
+                StreamSegment::Think(s) => buffer.insert_with_tags(iter, &s, &[&self.think_tag]),
+                StreamSegment::ThinkEnd => buffer.insert(iter, "\n\n"),
             }
         }
-        
         result
     }
     
@@ -382,6 +345,68 @@ impl MarkdownRenderer {
     }
 }
 
+/// A parsed segment from streaming think-tag processing.
+///
+/// Separating the pure detection logic (see [`parse_think_segments`]) from GTK mutations lets us
+/// unit-test the state machine without a live display session.
+#[derive(Debug, PartialEq)]
+enum StreamSegment {
+    /// Plain text that passes through the markdown renderer.
+    Normal(String),
+    /// The `<think>` opening boundary was seen; the GTK layer emits an indicator.
+    ThinkStart,
+    /// Content inside a think block, rendered with the think-tag style.
+    Think(String),
+    /// The `</think>` closing boundary was seen; the GTK layer emits a separator.
+    ThinkEnd,
+}
+
+/// Parse `text` into typed [`StreamSegment`]s, updating the in-flight `in_think` cursor.
+///
+/// Streaming-safe: a think block may open in one call and close in a later call.
+fn parse_think_segments(text: &str, in_think: &mut bool) -> Vec<StreamSegment> {
+    let mut segments = Vec::new();
+    let mut remaining = text;
+
+    while !remaining.is_empty() {
+        if *in_think {
+            match remaining.find("</think>") {
+                Some(end_pos) => {
+                    let content = &remaining[..end_pos];
+                    if !content.is_empty() {
+                        segments.push(StreamSegment::Think(content.to_string()));
+                    }
+                    segments.push(StreamSegment::ThinkEnd);
+                    *in_think = false;
+                    remaining = &remaining[end_pos + 8..]; // skip "</think>"
+                }
+                None => {
+                    segments.push(StreamSegment::Think(remaining.to_string()));
+                    break;
+                }
+            }
+        } else {
+            match remaining.find("<think>") {
+                Some(start_pos) => {
+                    let before = &remaining[..start_pos];
+                    if !before.is_empty() {
+                        segments.push(StreamSegment::Normal(before.to_string()));
+                    }
+                    segments.push(StreamSegment::ThinkStart);
+                    *in_think = true;
+                    remaining = &remaining[start_pos + 7..]; // skip "<think>"
+                }
+                None => {
+                    segments.push(StreamSegment::Normal(remaining.to_string()));
+                    break;
+                }
+            }
+        }
+    }
+
+    segments
+}
+
 /// Helper function to parse color strings (hex format) into RGBA
 fn parse_color(color_str: &str) -> Result<gtk4::gdk::RGBA, Box<dyn std::error::Error>> {
     let color_str = color_str.trim_start_matches('#');
@@ -395,4 +420,131 @@ fn parse_color(color_str: &str) -> Result<gtk4::gdk::RGBA, Box<dyn std::error::E
     let b = u8::from_str_radix(&color_str[4..6], 16)? as f32 / 255.0;
     
     Ok(gtk4::gdk::RGBA::new(r, g, b, 1.0))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // ── parse_color ──────────────────────────────────────────────────────────
+
+    #[test]
+    fn parse_color_red() {
+        let c = parse_color("#ff0000").unwrap();
+        assert!((c.red() - 1.0).abs() < 1e-4);
+        assert!((c.green() - 0.0).abs() < 1e-4);
+        assert!((c.blue() - 0.0).abs() < 1e-4);
+        assert!((c.alpha() - 1.0).abs() < 1e-4);
+    }
+
+    #[test]
+    fn parse_color_black() {
+        let c = parse_color("#000000").unwrap();
+        assert!((c.red() - 0.0).abs() < 1e-4);
+        assert!((c.green() - 0.0).abs() < 1e-4);
+        assert!((c.blue() - 0.0).abs() < 1e-4);
+    }
+
+    #[test]
+    fn parse_color_white() {
+        let c = parse_color("#ffffff").unwrap();
+        assert!((c.red() - 1.0).abs() < 1e-4);
+        assert!((c.green() - 1.0).abs() < 1e-4);
+        assert!((c.blue() - 1.0).abs() < 1e-4);
+    }
+
+    #[test]
+    fn parse_color_short_hex_is_error() {
+        assert!(parse_color("#fff").is_err());
+    }
+
+    #[test]
+    fn parse_color_non_hex_chars_is_error() {
+        assert!(parse_color("#zzzzzz").is_err());
+    }
+
+    #[test]
+    fn parse_color_empty_is_error() {
+        assert!(parse_color("").is_err());
+    }
+
+    // ── parse_think_segments ─────────────────────────────────────────────────
+
+    #[test]
+    fn plain_text_produces_single_normal_segment() {
+        let mut in_think = false;
+        let segs = parse_think_segments("hello world", &mut in_think);
+        assert_eq!(segs, vec![StreamSegment::Normal("hello world".into())]);
+        assert!(!in_think);
+    }
+
+    #[test]
+    fn think_block_in_middle_produces_all_segments() {
+        let mut in_think = false;
+        let segs = parse_think_segments("before <think>thinking</think> after", &mut in_think);
+        assert_eq!(segs, vec![
+            StreamSegment::Normal("before ".into()),
+            StreamSegment::ThinkStart,
+            StreamSegment::Think("thinking".into()),
+            StreamSegment::ThinkEnd,
+            StreamSegment::Normal(" after".into()),
+        ]);
+        assert!(!in_think);
+    }
+
+    #[test]
+    fn unclosed_think_tag_leaves_in_think_true() {
+        let mut in_think = false;
+        let segs = parse_think_segments("start <think>partial", &mut in_think);
+        assert_eq!(segs, vec![
+            StreamSegment::Normal("start ".into()),
+            StreamSegment::ThinkStart,
+            StreamSegment::Think("partial".into()),
+        ]);
+        assert!(in_think);
+    }
+
+    #[test]
+    fn closing_tag_in_second_call_closes_correctly() {
+        let mut in_think = true; // simulate carrying over from previous call
+        let segs = parse_think_segments("rest</think> normal", &mut in_think);
+        assert_eq!(segs, vec![
+            StreamSegment::Think("rest".into()),
+            StreamSegment::ThinkEnd,
+            StreamSegment::Normal(" normal".into()),
+        ]);
+        assert!(!in_think);
+    }
+
+    #[test]
+    fn continuation_while_in_think_produces_think_segment() {
+        let mut in_think = true;
+        let segs = parse_think_segments("more thinking...", &mut in_think);
+        assert_eq!(segs, vec![StreamSegment::Think("more thinking...".into())]);
+        assert!(in_think);
+    }
+
+    #[test]
+    fn empty_think_block_produces_start_and_end_only() {
+        let mut in_think = false;
+        let segs = parse_think_segments("<think></think>", &mut in_think);
+        assert_eq!(segs, vec![
+            StreamSegment::ThinkStart,
+            StreamSegment::ThinkEnd,
+        ]);
+        assert!(!in_think);
+    }
+
+    #[test]
+    fn think_block_at_very_start() {
+        let mut in_think = false;
+        let segs = parse_think_segments("<think>reasoning</think>answer", &mut in_think);
+        assert_eq!(segs, vec![
+            StreamSegment::ThinkStart,
+            StreamSegment::Think("reasoning".into()),
+            StreamSegment::ThinkEnd,
+            StreamSegment::Normal("answer".into()),
+        ]);
+        assert!(!in_think);
+    }
 }
\ No newline at end of file
diff --git a/src/state.rs b/src/state.rs
index 0a470e4..c41e113 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -107,5 +107,109 @@ impl AppState {
         self.set_generating(false);
         self.set_status("Generation stopped".to_string());
     }
-    
+
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn make_state() -> AppState {
+        AppState {
+            conversation: Vec::new(),
+            ollama_url: "http://localhost:11434".into(),
+            is_generating: false,
+            button_state: ButtonState::Send,
+            current_task: None,
+            selected_model: None,
+            status_message: "Ready".into(),
+            system_prompt: None,
+            config: Config::default(),
+        }
+    }
+
+    #[test]
+    fn set_generating_true_sets_stop_state() {
+        let mut state = make_state();
+        state.set_generating(true);
+        assert!(state.is_generating);
+        assert_eq!(state.button_state, ButtonState::Stop);
+    }
+
+    #[test]
+    fn set_generating_false_sets_send_state() {
+        let mut state = make_state();
+        state.is_generating = true;
+        state.button_state = ButtonState::Stop;
+        state.set_generating(false);
+        assert!(!state.is_generating);
+        assert_eq!(state.button_state, ButtonState::Send);
+    }
+
+    #[test]
+    fn add_user_message_appends_with_correct_role() {
+        let mut state = make_state();
+        state.add_user_message("hello".into());
+        assert_eq!(state.conversation.len(), 1);
+        assert_eq!(state.conversation[0].role, "user");
+        assert_eq!(state.conversation[0].content, "hello");
+    }
+
+    #[test]
+    fn add_assistant_message_appends_with_correct_role() {
+        let mut state = make_state();
+        state.add_assistant_message("hi there".into());
+        assert_eq!(state.conversation.len(), 1);
+        assert_eq!(state.conversation[0].role, "assistant");
+        assert_eq!(state.conversation[0].content, "hi there");
+    }
+
+    #[test]
+    fn conversation_preserves_insertion_order() {
+        let mut state = make_state();
+        state.add_user_message("first".into());
+        state.add_assistant_message("second".into());
+        state.add_user_message("third".into());
+        assert_eq!(state.conversation.len(), 3);
+        assert_eq!(state.conversation[0].role, "user");
+        assert_eq!(state.conversation[1].role, "assistant");
+        assert_eq!(state.conversation[2].role, "user");
+    }
+
+    #[test]
+    fn set_status_updates_message() {
+        let mut state = make_state();
+        state.set_status("Loading models...".into());
+        assert_eq!(state.status_message, "Loading models...");
+    }
+
+    #[test]
+    fn abort_current_task_without_task_resets_state() {
+        let mut state = make_state();
+        state.is_generating = true;
+        state.button_state = ButtonState::Stop;
+        state.abort_current_task();
+        assert!(!state.is_generating);
+        assert_eq!(state.button_state, ButtonState::Send);
+        assert_eq!(state.status_message, "Generation stopped");
+        assert!(state.current_task.is_none());
+    }
+
+    #[tokio::test]
+    async fn abort_current_task_aborts_running_task() {
+        let mut state = make_state();
+        // Spawn a task that sleeps forever so we can verify it gets aborted
+        let handle = tokio::spawn(async {
+            tokio::time::sleep(tokio::time::Duration::from_secs(3600)).await;
+        });
+        state.current_task = Some(handle);
+        state.is_generating = true;
+        state.button_state = ButtonState::Stop;
+
+        state.abort_current_task();
+
+        assert!(state.current_task.is_none());
+        assert!(!state.is_generating);
+        assert_eq!(state.status_message, "Generation stopped");
+    }
 }
\ No newline at end of file
diff --git a/src/types.rs b/src/types.rs
index 1a16ef1..0da4dbe 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -1,5 +1,7 @@
 use serde::{Deserialize, Serialize};
 
+// --- Types ---
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ChatMessage {
     pub role: String,
@@ -36,4 +38,47 @@ pub struct ModelInfo {
 #[derive(Debug, Serialize, Deserialize)]
 pub struct ModelsResponse {
     pub models: Vec<ModelInfo>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // `cargo test` will run these. This is the standard Rust pattern:
+    // put tests in a `#[cfg(test)]` module so they're compiled only when testing.
+
+    #[test]
+    fn chat_message_serializes_and_deserializes() {
+        // Verify that serde roundtrips correctly — if you ever rename a field
+        // or change its type, this test catches it before it reaches the API.
+        let msg = ChatMessage {
+            role: "user".to_string(),
+            content: "Hello, world!".to_string(),
+        };
+        let json = serde_json::to_string(&msg).unwrap();
+        let decoded: ChatMessage = serde_json::from_str(&json).unwrap();
+        assert_eq!(decoded.role, msg.role);
+        assert_eq!(decoded.content, msg.content);
+    }
+
+    #[test]
+    fn chat_request_includes_stream_flag() {
+        let req = ChatRequest {
+            model: "llama3".to_string(),
+            messages: vec![],
+            stream: true,
+        };
+        let json = serde_json::to_string(&req).unwrap();
+        // The Ollama API requires `"stream": true` in the body.
+        assert!(json.contains("\"stream\":true"));
+    }
+
+    #[test]
+    fn stream_response_parses_done_flag() {
+        // Real payload shape from the Ollama streaming API.
+        let raw = r#"{"model":"llama3","created_at":"2024-01-01T00:00:00Z","message":{"role":"assistant","content":"Hi"},"done":true}"#;
+        let resp: StreamResponse = serde_json::from_str(raw).unwrap();
+        assert!(resp.done);
+        assert_eq!(resp.message.content, "Hi");
+    }
 }
\ No newline at end of file
diff --git a/src/ui/handlers.rs b/src/ui/handlers.rs
index 0dc68c9..8603f64 100644
--- a/src/ui/handlers.rs
+++ b/src/ui/handlers.rs
@@ -243,7 +243,6 @@ fn setup_streaming_handlers(
             accumulated_content.push_str(&content_batch);
             let config = shared_state_streaming.borrow().config.clone();
             chat_view_content.update_streaming_markdown(&response_mark_clone, &accumulated_content, &config);
-            chat_view_content.scroll_to_bottom();
         }
     });