Assert #658 works (#945)

* assert #658 works

* fix linting

tests_functional/issues/658_nested_envvar_override/Makefile

@@ -0,0 +1,4 @@
+.PHONY: test
+
+test:
+	pytest -v app_test.py

tests_functional/issues/658_nested_envvar_override/app_test.py

@@ -0,0 +1,60 @@
+"""
+Given:
+- loaded settings file with three nested levels a.b.c
+When
+- override nested value (a.b.c) with envvar loading
+Should
+- access the new value case-insensitive (a.b.c == A.B.C)
+Instead
+- lowercase override doesn't work, while uppercase work
+
+https://github.com/dynaconf/dynaconf/issues/658
+"""
+from __future__ import annotations
+
+from textwrap import dedent
+
+from dynaconf import Dynaconf
+
+
+def create_file(filename: str, data: str):
+    """Utility to write files"""
+    with open(filename, "w") as f:
+        f.write(dedent(data))
+    return filename
+
+
+def new_settings(tmp_path):
+    """Common setup for tests"""
+    # settings file used
+    filename = create_file(
+        tmp_path / "s.yaml",
+        """\
+        a:
+          b: foo
+          c:
+            d: hello
+        """,
+    )
+
+    # setup
+    return Dynaconf(
+        envvar_prefix="DYNACONF",
+        settings_files=filename,
+    )
+
+
+def test_nested_one_uppercase(monkeypatch, tmp_path):
+    monkeypatch.setenv("DYNACONF_A__B", "OK")
+    assert new_settings(tmp_path).a.b == "OK"
+
+
+def test_nested_two_lowercase(monkeypatch, tmp_path):
+    monkeypatch.setenv("DYNACONF_a__b__c", "OK")
+    assert new_settings(tmp_path).a.b.c == "OK"
+
+
+def test_nested_two_uppercase(monkeypatch, tmp_path):
+    monkeypatch.setenv("DYNACONF_A__B__C", "OK")
+    assert new_settings(tmp_path).A.B.C == "OK"
+    assert new_settings(tmp_path).a.b.c == "OK"  # failed before