[css] Add a test for the impact of our border edge types on the layout

tests/test_integration_layout.py

@@ -3,9 +3,12 @@ import asyncio
 from typing import cast, List
 
 import pytest
+from rich.console import RenderableType
+from rich.text import Text
 
 from tests.utilities.test_app import AppTest
 from textual.app import ComposeResult
+from textual.css.types import EdgeType
 from textual.geometry import Size
 from textual.widget import Widget
 from textual.widgets import Placeholder
@@ -31,30 +34,20 @@ PLACEHOLDERS_DEFAULT_H = 3  # the default height for our Placeholder widgets
         "expected_placeholders_offset_x",
     ),
     (
-        [
-            SCREEN_SIZE,
-            1,
-            "border: ;",  # #root has no border
-            "",  # no specific placeholder style
-            # #root's virtual size=screen size
-            (SCREEN_W, SCREEN_H),
-            # placeholders width=same than screen :: height=default height
-            (SCREEN_W, PLACEHOLDERS_DEFAULT_H),
-            # placeholders should be at offset 0
-            0,
-        ],
-        [
-            # "none" borders still allocate a space for the (invisible) border
-            SCREEN_SIZE,
-            1,
-            "border: none;",  # #root has an invisible border
-            "",  # no specific placeholder style
-            # #root's virtual size is smaller because of its borders
-            (SCREEN_W - 2, SCREEN_H - 2),
-            # placeholders width=same than screen, minus 2 borders :: height=default height minus 2 borders
-            (SCREEN_W - 2, PLACEHOLDERS_DEFAULT_H),
-            # placeholders should be at offset 1 because of #root's border
-            1,
+        *[
+            [
+                SCREEN_SIZE,
+                1,
+                f"border: {invisible_border_edge};",  # #root has no visible border
+                "",  # no specific placeholder style
+                # #root's virtual size=screen size
+                (SCREEN_W, SCREEN_H),
+                # placeholders width=same than screen :: height=default height
+                (SCREEN_W, PLACEHOLDERS_DEFAULT_H),
+                # placeholders should be at offset 0
+                0,
+            ]
+            for invisible_border_edge in ("", "none", "hidden")
         ],
         [
             SCREEN_SIZE,
@@ -169,3 +162,75 @@ async def test_composition_of_vertical_container_with_children(
         assert placeholder.size == expected_placeholders_size
         assert placeholder.styles.offset.x.value == 0.0
         assert app.screen.get_offset(placeholder).x == expected_placeholders_offset_x
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration_test
+@pytest.mark.parametrize(
+    "edge_type,expected_box_inner_size,expected_box_size,expected_top_left_edge_color,expects_visible_char_at_top_left_edge",
+    (
+        # These first 3 types of border edge types are synonyms, and display no borders:
+        ["", Size(SCREEN_W, 1), Size(SCREEN_W, 1), "black", False],
+        ["none", Size(SCREEN_W, 1), Size(SCREEN_W, 1), "black", False],
+        ["hidden", Size(SCREEN_W, 1), Size(SCREEN_W, 1), "black", False],
+        # Let's transition to "blank": we still see no visible border, but the size is increased
+        # as the gutter space is reserved the same way it would be with a border:
+        ["blank", Size(SCREEN_W - 2, 1), Size(SCREEN_W, 3), "#ffffff", False],
+        # And now for the "normally visible" border edge types:
+        # --> we see a visible border, and the size is increased:
+        *[
+            [edge_style, Size(SCREEN_W - 2, 1), Size(SCREEN_W, 3), "#ffffff", True]
+            for edge_style in [
+                "round",
+                "solid",
+                "double",
+                "dashed",
+                "heavy",
+                "inner",
+                "outer",
+                "hkey",
+                "vkey",
+                "tall",
+                "wide",
+            ]
+        ],
+    ),
+)
+async def test_border_edge_types_impact_on_widget_size(
+    edge_type: EdgeType,
+    expected_box_inner_size: Size,
+    expected_box_size: Size,
+    expected_top_left_edge_color: str,
+    expects_visible_char_at_top_left_edge: bool,
+):
+    class BorderTarget(Widget):
+        def render(self, style) -> RenderableType:
+            return Text("border target", style="black on yellow", justify="center")
+
+    border_target = BorderTarget()
+    border_target.styles.height = "auto"
+    border_target.styles.border = (edge_type, "white")
+
+    class MyTestApp(AppTest):
+        def compose(self) -> ComposeResult:
+            yield border_target
+
+    app = MyTestApp(size=SCREEN_SIZE, test_name="border_edge_types")
+
+    await app.boot_and_shutdown()
+
+    box_inner_size = Size(
+        border_target.content_region.width,
+        border_target.content_region.height,
+    )
+    assert box_inner_size == expected_box_inner_size
+
+    assert border_target.size == expected_box_size
+
+    top_left_edge_style = app.screen.get_style_at(0, 0)
+    top_left_edge_color = top_left_edge_style.color.name
+    assert top_left_edge_color == expected_top_left_edge_color
+
+    top_left_edge_char = app.get_char_at(0, 0)
+    top_left_edge_char_is_a_visible_one = top_left_edge_char != " "
+    assert top_left_edge_char_is_a_visible_one == expects_visible_char_at_top_left_edge