added challenge integration test

Cargo.toml

@@ -34,3 +34,4 @@ opt-level = 3
 
 [dev-dependencies]
 axum-test = "14"
+http = "1"

tests/integration_tests.rs

@@ -1,13 +1,14 @@
 use axum_test::{TestServer, TestServerConfig};
+use hmac::{Hmac, Mac};
+use http::{HeaderName, HeaderValue};
 use rust_slackbot_llm::routes::create_routes;
-use serde_json::Value;
+use serde_json::{json, Value};
+use sha2::Sha256;
+use std::{fmt::Write, time::SystemTime};
 
 async fn new_test_app() -> TestServer {
     let app = create_routes().await.unwrap();
-    let config = TestServerConfig::builder()
-        .expect_success_by_default()
-        .mock_transport()
-        .build();
+    let config = TestServerConfig::builder().mock_transport().build();
 
     TestServer::new_with_config(app, config).unwrap()
 }
@@ -22,3 +23,53 @@ async fn test_index() {
     let expected_response: Value = "Welcome to the Rust Slackbot LLM API!".into();
     response.assert_json(&expected_response);
 }
+
+#[tokio::test]
+async fn test_challenge() {
+    let slack_signing_secret = "some_signing_secret";
+    std::env::set_var("SLACK_SIGNING_SECRET", slack_signing_secret);
+
+    let server = new_test_app().await;
+    let now = std::time::SystemTime::now()
+        .duration_since(SystemTime::UNIX_EPOCH)
+        .unwrap()
+        .as_secs() as f64;
+    let now = now.to_string();
+    let payload = json!({
+        "token": "some_token",
+        "challenge": "some_challenge",
+        "type": "url_verification",
+    });
+
+    let body = payload.to_string();
+    let body = "v0:".to_owned() + now.as_str() + ":" + body.as_str();
+
+    let mut mac = Hmac::<Sha256>::new_from_slice(slack_signing_secret.as_bytes())
+        .expect("HMAC can take key of any size");
+    mac.update(body.as_bytes());
+    let mac_result = mac.finalize();
+    let slack_signature = mac_result.into_bytes();
+    let slack_signature = slack_signature.iter().fold(String::new(), |mut output, b| {
+        let _ = write!(output, "{b:02x}");
+        output
+    });
+    let slack_signature = "v0=".to_owned() + slack_signature.as_str();
+
+    let response = server
+        .post("/v1/slack_events")
+        .json(&payload)
+        .add_header(
+            HeaderName::from_static("x-slack-request-timestamp"),
+            HeaderValue::from_str(now.as_str()).unwrap(),
+        )
+        .add_header(
+            HeaderName::from_static("x-slack-signature"),
+            HeaderValue::from_str(slack_signature.as_str()).unwrap(),
+        )
+        .await;
+
+    response.assert_json(&json!({
+        "challenge": "some_challenge",
+    }));
+    assert_eq!(response.status_code(), 200);
+}