From 66fa0020e8ccc0a48e06b7b8f6c115f64d1be9bc Mon Sep 17 00:00:00 2001
From: Darren Burns <darrenb900@gmail.com>
Date: Mon, 14 Feb 2022 10:28:52 +0000
Subject: [PATCH] Improve a docstring, add tests for CSS opacity parsing

---
 src/textual/css/_styles_builder.py |  3 ++-
 tests/css/test_parse.py            | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/textual/css/_styles_builder.py b/src/textual/css/_styles_builder.py
index c3dc6cf6f..005e5f2ea 100644
--- a/src/textual/css/_styles_builder.py
+++ b/src/textual/css/_styles_builder.py
@@ -21,10 +21,11 @@ from ..geometry import Spacing, SpacingDimensions, clamp
 
 
 def _join_tokens(tokens: Iterable[Token], joiner: str = "") -> str:
-    """Convert tokens into a string
+    """Convert tokens into a string by joining their values
 
     Args:
         tokens (Iterable[Token]): Tokens to join
+        joiner (str): String to join on, defaults to ""
 
     Returns:
         str: The tokens, joined together to form a string.
diff --git a/tests/css/test_parse.py b/tests/css/test_parse.py
index 5142d5cc9..10b54b502 100644
--- a/tests/css/test_parse.py
+++ b/tests/css/test_parse.py
@@ -314,3 +314,29 @@ class TestParseTransition:
         assert len(stylesheet_errors) == 1
         assert stylesheet_errors[0][0].value == invalid_func_name
         assert ex.value.errors is not None
+
+
+class TestParseOpacity:
+    @pytest.mark.parametrize("css_value, styles_value", [
+        ["-0.2", 0.0],
+        ["0.4", 0.4],
+        ["1.3", 1.0],
+        ["-20%", 0.0],
+        ["25%", 0.25],
+        ["128%", 1.0],
+    ])
+    def test_opacity_to_styles(self, css_value, styles_value):
+        css = f"#some-widget {{ opacity: {css_value} }}"
+        stylesheet = Stylesheet()
+        stylesheet.parse(css)
+
+        assert stylesheet.rules[0].styles.opacity == styles_value
+        assert not stylesheet.rules[0].errors
+
+    def test_opacity_invalid_value(self):
+        css = "#some-widget { opacity: 123x }"
+        stylesheet = Stylesheet()
+
+        with pytest.raises(StylesheetParseError):
+            stylesheet.parse(css)
+        assert stylesheet.rules[0].errors