Add tests for @extend newline error.

js/test/generated/beautify-css-tests.js

@@ -10747,6 +10747,10 @@ function run_css_tests(test_obj, Urlencoded, js_beautify, html_beautify, css_bea
             '.item-warning-wrong {\n' +
             '    @extend btn-warning: hover;\n' +
             '}');
+        t(
+            '.item-warning {\n' +
+            '    @extend .color1, .hover2;\n' +
+            '}');
 
 
         //============================================================

python/cssbeautifier/tests/generated/tests.py

@@ -10626,6 +10626,10 @@ class CSSBeautifierTest(unittest.TestCase):
             '.item-warning-wrong {\n' +
             '    @extend btn-warning: hover;\n' +
             '}')
+        t(
+            '.item-warning {\n' +
+            '    @extend .color1, .hover2;\n' +
+            '}')
 
 
         #============================================================

test/data/css/tests.js

@@ -1559,6 +1559,12 @@ exports.test_data = {
           '    @extend btn-warning: hover;',
           '}'
         ]
+      }, {
+        unchanged: [
+          '.item-warning {',
+          '    @extend .color1, .hover2;',
+          '}'
+        ]
       }]
     }, {
       name: "Import Tests",