test mime sniff for unknown ext

Author: yoshuawuyts

tests/fixtures/unknown.custom_ext

@@ -0,0 +1 @@
+this is an unknown text format

tests/mime.rs

@@ -18,3 +18,12 @@ async fn guess_binary_mime() -> io::Result<()> {
     assert_eq!(res.content_type(), Some(mime::PNG));
     Ok(())
 }
+
+#[async_std::test]
+async fn guess_mime_fallback() -> io::Result<()> {
+    let body = Body::from_file("tests/fixtures/unknown.custom_ext").await?;
+    let mut res = Response::new(200);
+    res.set_body(body);
+    assert_eq!(res.content_type(), Some(mime::BYTE_STREAM));
+    Ok(())
+}