diff --git a/src/dc_msg.rs b/src/dc_msg.rs
index 6e03e9b88..cf07ba795 100644
--- a/src/dc_msg.rs
+++ b/src/dc_msg.rs
@@ -1616,3 +1616,36 @@ pub unsafe fn dc_update_server_uid(
     sqlite3_step(stmt);
     sqlite3_finalize(stmt);
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::ffi::CStr;
+
+    #[test]
+    fn test_dc_msg_guess_msgtype_from_suffix() {
+        unsafe {
+            let mut type_0: libc::c_int = 0;
+            let mut mime_0: *mut libc::c_char = 0 as *mut libc::c_char;
+            dc_msg_guess_msgtype_from_suffix(
+                b"foo/bar-sth.mp3\x00" as *const u8 as *const libc::c_char,
+                0 as *mut libc::c_int,
+                &mut mime_0,
+            );
+            assert_eq!(
+                CStr::from_ptr(mime_0 as *const libc::c_char)
+                    .to_str()
+                    .unwrap(),
+                "audio/mpeg"
+            );
+            dc_msg_guess_msgtype_from_suffix(
+                b"foo/bar-sth.mp3\x00" as *const u8 as *const libc::c_char,
+                &mut type_0,
+                0 as *mut *mut libc::c_char,
+            );
+            assert_eq!(type_0, 40);
+            // TODO add more tests for different message types
+            free(mime_0 as *mut libc::c_void);
+        }
+    }
+}
diff --git a/tests/stress.rs b/tests/stress.rs
index 8f250efa2..ae1eb2091 100644
--- a/tests/stress.rs
+++ b/tests/stress.rs
@@ -17,7 +17,6 @@ use deltachat::dc_keyring::*;
 use deltachat::dc_location::*;
 use deltachat::dc_lot::*;
 use deltachat::dc_mimeparser::*;
-use deltachat::dc_msg::*;
 use deltachat::dc_param::*;
 use deltachat::dc_pgp::*;
 use deltachat::dc_qr::*;
@@ -415,49 +414,6 @@ unsafe fn stress_functions(context: &dc_context_t) {
         free(fn1 as *mut libc::c_void);
     }
 
-    let mut type_0: libc::c_int = 0;
-    let mut mime_0: *mut libc::c_char = 0 as *mut libc::c_char;
-    dc_msg_guess_msgtype_from_suffix(
-        b"foo/bar-sth.mp3\x00" as *const u8 as *const libc::c_char,
-        0 as *mut libc::c_int,
-        0 as *mut *mut libc::c_char,
-    );
-    dc_msg_guess_msgtype_from_suffix(
-        b"foo/bar-sth.mp3\x00" as *const u8 as *const libc::c_char,
-        0 as *mut libc::c_int,
-        &mut mime_0,
-    );
-    if 0 != !(strcmp(
-        mime_0,
-        b"audio/mpeg\x00" as *const u8 as *const libc::c_char,
-    ) == 0i32) as libc::c_int as libc::c_long
-    {
-        __assert_rtn(
-            (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
-                .as_ptr(),
-            b"../cmdline/stress.c\x00" as *const u8 as *const libc::c_char,
-            360i32,
-            b"strcmp(mime, \"audio/mpeg\")==0\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    dc_msg_guess_msgtype_from_suffix(
-        b"foo/bar-sth.mp3\x00" as *const u8 as *const libc::c_char,
-        &mut type_0,
-        0 as *mut *mut libc::c_char,
-    );
-    if 0 != !(type_0 == 40i32) as libc::c_int as libc::c_long {
-        __assert_rtn(
-            (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
-                .as_ptr(),
-            b"../cmdline/stress.c\x00" as *const u8 as *const libc::c_char,
-            362i32,
-            b"type == DC_MSG_AUDIO\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    free(mime_0 as *mut libc::c_void);
-
     let mut str: *mut libc::c_char = strdup(b"aaa\x00" as *const u8 as *const libc::c_char);
     let replacements: libc::c_int = dc_str_replace(
         &mut str,