Test coverage: add asynchronous native-environment string concatenati…

…on case

Adds additional test coverage for #1511

tests/test_nativetypes.py

@@ -13,6 +13,11 @@ def env():
     return NativeEnvironment()
 
 
+@pytest.fixture
+def async_native_env():
+    return NativeEnvironment(enable_async=True)
+
+
 def test_is_defined_native_return(env):
     t = env.from_string("{{ missing is defined }}")
     assert not t.render()
@@ -122,6 +127,16 @@ def test_string_top_level(env):
     assert result == "Jinja"
 
 
+@pytest.mark.asyncio
+async def test_string_concatenation(async_native_env):
+    t = async_native_env.from_string(
+        "{%- macro x(y) -%}{{ y }}{%- endmacro -%}{{- x('not') }} {{ x('bad') -}}"
+    )
+    result = await t.render_async()
+    assert isinstance(result, str)
+    assert result == "not bad"
+
+
 def test_tuple_of_variable_strings(env):
     t = env.from_string("'{{ a }}', 'data', '{{ b }}', b'{{ c }}'")
     result = t.render(a=1, b=2, c="bytes")