Test the exception message.

Also make it more useful.

And add additional test data to fully exercise the code.

Author: JakeQZ

src/RuleSet/DeclarationBlock.php

@@ -101,11 +101,22 @@ public function setSelectors($selectors, ?CSSList $list = null): void
         } else {
             // A string of comma-separated selectors requires parsing.
             // Parse as if it's the opening part of a rule.
-            $parserState = new ParserState($selectors . '{', Settings::create());
-            $selectorsToSet = self::parseSelectors($parserState);
-            $parserState->consume('{'); // throw exception if this is not next
-            if (!$parserState->isEnd()) {
-                throw new UnexpectedTokenException('EOF', $parserState->peek(5));
+            try {
+                $parserState = new ParserState($selectors . '{', Settings::create());
+                $selectorsToSet = self::parseSelectors($parserState);
+                $parserState->consume('{'); // throw exception if this is not next
+                if (!$parserState->isEnd()) {
+                    throw new UnexpectedTokenException('EOF', 'more');
+                }
+            } catch (UnexpectedTokenException $exception) {
+                // The exception message from parsing may refer to the faux `{` block start token,
+                // which would be confusing.
+                // Rethrow with a more useful message, that also includes the selector(s) string that was passed.
+                throw new UnexpectedTokenException(
+                    'Selector(s) string is not valid.',
+                    $selectors,
+                    'custom'
+                );
             }
         }
 

tests/Unit/RuleSet/DeclarationBlockTest.php

@@ -333,16 +333,31 @@ public function setSelectorsSetsTwoCommaSeparatedSelectorsProvidedAsString(
         self::assertSame([$firstSelector, $secondSelector], self::getSelectorsAsStrings($subject));
     }
 
+    /**
+     * Provides selectors that would be parsed without error in the context of full CSS, but are nonetheless invalid.
+     *
+     * @return array<non-empty-string, array{0: non-empty-string}>
+     */
+    public static function provideInvalidStandaloneSelector(): array
+    {
+        return [
+            'rogue `{`' => ['a { b'],
+            'rogue `}`' => ['a } b'],
+        ];
+    }
+
     /**
      * @test
      *
      * @param non-empty-string $selector
      *
      * @dataProvider provideInvalidSelector
+     * @dataProvider provideInvalidStandaloneSelector
      */
     public function setSelectorsThrowsExceptionWithInvalidSelector(string $selector): void
     {
         $this->expectException(UnexpectedTokenException::class);
+        $this->expectExceptionMessageMatches('/^Selector\\(s\\) string is not valid. /');
 
         $subject = new DeclarationBlock();