Use render instead of render_lines in Opacity, add tests

tests/renderables/test_opacity.py

@@ -4,28 +4,47 @@ from rich.text import Text
 from tests.utilities.render import render
 from textual.renderables.opacity import Opacity
 
-
-@pytest.mark.skip
-def test_simple_opacity():
-    text = Text("Hello, world!", style="#ff0000 on #00ff00")
-    assert render(Opacity(text, value=.5)) == ""
+STOP = "\x1b[0m"
 
 
-@pytest.mark.skip
-def test_ansi_colors_ignored():
-    pass
+@pytest.fixture
+def text():
+    return Text("Hello, world!", style="#ff0000 on #00ff00", end="")
 
 
-@pytest.mark.skip
-def test_opacity_no_style():
-    pass
+def test_simple_opacity(text):
+    blended_red_on_green = "\x1b[38;2;127;127;0;48;2;0;255;0m"
+    assert render(Opacity(text, value=.5)) == (
+        f"{blended_red_on_green}Hello, world!{STOP}"
+    )
 
 
-@pytest.mark.skip
-def test_opacity_only_fg():
-    pass
+def test_value_zero_sets_foreground_color_to_background_color(text):
+    foreground = background = "0;255;0"
+    assert render(Opacity(text, value=0)) == (
+        f"\x1b[38;2;{foreground};48;2;{background}mHello, world!{STOP}"
+    )
 
 
-@pytest.mark.skip
-def test_opacity_only_bg():
-    pass
+def test_opacity_value_of_one_noop(text):
+    assert render(Opacity(text, value=1)) == render(text)
+
+
+def test_ansi_colors_noop():
+    ansi_colored_text = Text("Hello, world!", style="red on green", end="")
+    assert render(Opacity(ansi_colored_text, value=.5)) == render(ansi_colored_text)
+
+
+def test_opacity_no_style_noop():
+    text_no_style = Text("Hello, world!", end="")
+    assert render(Opacity(text_no_style, value=.2)) == render(text_no_style)
+
+
+def test_opacity_only_fg_noop():
+    text_only_fg = Text("Hello, world!", style="#ff0000", end="")
+    assert render(Opacity(text_only_fg, value=.5)) == render(text_only_fg)
+
+
+def test_opacity_only_bg_noop():
+    text_only_bg = Text("Hello, world!", style="on #ff0000", end="")
+    assert render(Opacity(text_only_bg, value=.5)) == render(text_only_bg)