tests/env: add empty name test

tests/by-util/test_env.rs

@@ -108,6 +108,15 @@ fn test_ignore_environment() {
     scene.ucmd().arg("-").run().no_stdout();
 }
 
+#[test]
+fn test_empty_name() {
+    new_ucmd!()
+        .arg("-i")
+        .arg("=xyz")
+        .run()
+        .stderr_only("env: warning: no name specified for value 'xyz'");
+}
+
 #[test]
 fn test_null_delimiter() {
     let out = new_ucmd!()