Invisible widgets now dont render

tests/test_widget.py

@@ -0,0 +1,28 @@
+import pytest
+
+from textual.css.errors import StyleValueError
+from textual.widget import Widget
+
+
+@pytest.mark.parametrize(
+    "set_val, get_val, style_str", [
+        [True, True, "visible"],
+        [False, False, "hidden"],
+        ["hidden", False, "hidden"],
+        ["visible", True, "visible"],
+    ])
+def test_widget_set_visible_true(set_val, get_val, style_str):
+    widget = Widget()
+    widget.visible = set_val
+
+    assert widget.visible is get_val
+    assert widget.styles.visibility == style_str
+
+
+def test_widget_set_visible_invalid_string():
+    widget = Widget()
+
+    with pytest.raises(StyleValueError):
+        widget.visible = "nope! no widget for me!"
+
+    assert widget.visible