3 files changed, 9 insertions, 2 deletions

diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 1aa1330a6..98ba05fc2 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -32,6 +32,7 @@ use hir_def::{
 use hir_expand::{diagnostics::DiagnosticSink, name::name};
 use ra_arena::map::ArenaMap;
 use ra_prof::profile;
+use test_utils::tested_by;
 
 use super::{
     primitive::{FloatTy, IntTy},
@@ -282,6 +283,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn insert_vars_for_impl_trait(&mut self, ty: Ty) -> Ty {
         ty.fold(&mut |ty| match ty {
             Ty::Opaque(preds) => {
+                tested_by!(insert_vars_for_impl_trait);
                 let var = self.table.new_type_var();
                 let var_subst = Substs::builder(1).push(var.clone()).build();
                 self.obligations.extend(
diff --git a/crates/ra_hir_ty/src/marks.rs b/crates/ra_hir_ty/src/marks.rs
index 0f754eb9c..fe74acf11 100644
--- a/crates/ra_hir_ty/src/marks.rs
+++ b/crates/ra_hir_ty/src/marks.rs
@@ -6,4 +6,5 @@ test_utils::marks!(
     type_var_resolves_to_int_var
     match_ergonomics_ref
     coerce_merge_fail_fallback
+    insert_vars_for_impl_trait
 );
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index d8673c90d..802937cb0 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -1,7 +1,10 @@
-use super::{infer, infer_with_mismatches, type_at, type_at_pos};
-use crate::test_db::TestDB;
 use insta::assert_snapshot;
+
 use ra_db::fixture::WithFixture;
+use test_utils::covers;
+
+use super::{infer, infer_with_mismatches, type_at, type_at_pos};
+use crate::test_db::TestDB;
 
 #[test]
 fn infer_await() {
@@ -1489,6 +1492,7 @@ fn test<T, U>() where T: Trait<U::Item>, U: Trait<T::Item> {
 
 #[test]
 fn unify_impl_trait() {
+    covers!(insert_vars_for_impl_trait);
     assert_snapshot!(
         infer_with_mismatches(r#"
 trait Trait<T> {}