Add snapshot test for tier-check

Author: Kobzol

src/bootstrap/src/core/builder/tests.rs

@@ -1930,6 +1930,19 @@ mod snapshot {
         ");
     }
 
+    #[test]
+    fn test_tier_check() {
+        let ctx = TestCtx::new();
+        insta::assert_snapshot!(
+            ctx.config("test")
+                .path("tier-check")
+                .render_steps(), @r"
+        [build] llvm <host>
+        [build] rustc 0 <host> -> rustc 1 <host>
+        [build] rustc 1 <host> -> std 1 <host>
+        ");
+    }
+
     #[test]
     fn doc_all() {
         let ctx = TestCtx::new();