features tests

tests/test_features.py

@@ -0,0 +1,22 @@
+from textual.app import App
+
+
+def test_env_vaer(monkeypatch):
+    monkeypatch.setenv("TEXTUAL", "")
+    app = App()
+    assert app.features == set()
+    assert app.devtools_enabled is False
+
+    monkeypatch.setenv("TEXTUAL", "devtools")
+    app = App()
+    assert app.features == {"devtools"}
+    assert app.devtools_enabled is True
+
+
+def test_devtools_enabled_property():
+
+    app = App(_features="")
+    assert app.devtools_enabled is False
+
+    app = App(_features="devtools")
+    assert app.devtools_enabled is True