(test) adding test for #433

tests/lookup_with_subexpression.rs

@@ -0,0 +1,31 @@
+use handlebars::{Context, Handlebars, Helper, HelperDef, RenderContext, RenderError, ScopedJson};
+use serde_json::json;
+
+struct MyHelper;
+
+impl HelperDef for MyHelper {
+    fn call_inner<'reg: 'rc, 'rc>(
+        &self,
+        _: &Helper<'reg, 'rc>,
+        _: &'reg Handlebars,
+        _: &'rc Context,
+        _: &mut RenderContext<'reg, 'rc>,
+    ) -> Result<Option<ScopedJson<'reg, 'rc>>, RenderError> {
+        Ok(Some(ScopedJson::Derived(json!({
+            "a": 1,
+            "b": 2,
+        }))))
+    }
+}
+
+#[test]
+fn test_lookup_with_subexpression() {
+    let mut registry = Handlebars::new();
+    registry.register_helper("myhelper", Box::new(MyHelper {}));
+
+    let result = registry
+        .render_template("{{ lookup (myhelper) \"a\" }}", &json!({}))
+        .unwrap();
+
+    assert_eq!("1", result);
+}