diff --git a/src/dc_contact.rs b/src/dc_contact.rs
index f786a3f72..1762ac468 100644
--- a/src/dc_contact.rs
+++ b/src/dc_contact.rs
@@ -45,7 +45,7 @@ pub unsafe fn dc_marknoticed_contact(context: &dc_context_t, contact_id: uint32_
     );
 }
 
-// handle contacts
+/// Returns false if addr is an invalid address, otherwise true.
 pub unsafe fn dc_may_be_valid_addr(addr: *const libc::c_char) -> bool {
     if addr.is_null() {
         return false;
@@ -1259,3 +1259,59 @@ pub unsafe fn dc_scaleup_contact_origin(
     sqlite3_step(stmt);
     sqlite3_finalize(stmt);
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_dc_may_be_valid_addr() {
+        unsafe {
+            assert_eq!(dc_may_be_valid_addr(0 as *const libc::c_char), false);
+            assert_eq!(
+                dc_may_be_valid_addr(b"\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"user@domain.tld\x00" as *const u8 as *const libc::c_char),
+                true
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"uuu\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"dd.tt\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"tt.dd@uu\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"u@d\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"u@d.\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"u@d.t\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"u@d.tt\x00" as *const u8 as *const libc::c_char),
+                true
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"u@.tt\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+            assert_eq!(
+                dc_may_be_valid_addr(b"@d.tt\x00" as *const u8 as *const libc::c_char),
+                false
+            );
+        }
+    }
+}
diff --git a/tests/stress.rs b/tests/stress.rs
index 21ddaba94..3e3112304 100644
--- a/tests/stress.rs
+++ b/tests/stress.rs
@@ -9,7 +9,6 @@ use tempfile::{tempdir, TempDir};
 use deltachat::constants::*;
 use deltachat::dc_array::*;
 use deltachat::dc_configure::*;
-use deltachat::dc_contact::*;
 use deltachat::dc_context::*;
 use deltachat::dc_hash::*;
 use deltachat::dc_imex::*;
@@ -592,160 +591,7 @@ unsafe fn stress_functions(context: &dc_context_t) {
     } else {
     };
     free(s as *mut libc::c_void);
-    if 0 != (dc_may_be_valid_addr(0 as *const libc::c_char)) 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,
-            380i32,
-            b"!dc_may_be_valid_addr(NULL)\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"\x00" as *const u8 as *const libc::c_char)) 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,
-            381i32,
-            b"!dc_may_be_valid_addr(\"\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (!dc_may_be_valid_addr(b"user@domain.tld\x00" as *const u8 as *const libc::c_char))
-        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,
-            382i32,
-            b"dc_may_be_valid_addr(\"user@domain.tld\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"uuu\x00" as *const u8 as *const libc::c_char)) 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,
-            383i32,
-            b"!dc_may_be_valid_addr(\"uuu\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"dd.tt\x00" as *const u8 as *const libc::c_char)) 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,
-            384i32,
-            b"!dc_may_be_valid_addr(\"dd.tt\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"tt.dd@uu\x00" as *const u8 as *const libc::c_char))
-        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,
-            385i32,
-            b"!dc_may_be_valid_addr(\"tt.dd@uu\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"uu\x00" as *const u8 as *const libc::c_char)) 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,
-            386i32,
-            b"!dc_may_be_valid_addr(\"uu\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"u@d\x00" as *const u8 as *const libc::c_char)) 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,
-            387i32,
-            b"!dc_may_be_valid_addr(\"u@d\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"u@d.\x00" as *const u8 as *const libc::c_char)) 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,
-            388i32,
-            b"!dc_may_be_valid_addr(\"u@d.\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"u@d.t\x00" as *const u8 as *const libc::c_char)) 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,
-            389i32,
-            b"!dc_may_be_valid_addr(\"u@d.t\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (!dc_may_be_valid_addr(b"u@d.tt\x00" as *const u8 as *const libc::c_char))
-        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,
-            390i32,
-            b"dc_may_be_valid_addr(\"u@d.tt\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"u@.tt\x00" as *const u8 as *const libc::c_char)) 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,
-            391i32,
-            b"!dc_may_be_valid_addr(\"u@.tt\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    if 0 != (dc_may_be_valid_addr(b"@d.tt\x00" as *const u8 as *const libc::c_char)) 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,
-            392i32,
-            b"!dc_may_be_valid_addr(\"@d.tt\")\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
+
     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,