Add a regression test for sass/dart-sass#2523

Author: nex3

spec/values/calculation/round/one_argument.hrx

@@ -135,6 +135,32 @@ DEPRECATION WARNING [slash-div]: Using / for division outside of calc() is depre
 
 Recommendation: math.div(2px, round(1.5)) or calc(2px / round(1.5))
 
+More info and automated migrator: https://sass-lang.com/d/slash-div
+
+  ,
+2 |   a: 2px / round(1.5);
+  |      ^^^^^^^^^^^^^^^^
+  '
+    input.scss 2:6  root stylesheet
+
+<===>
+================================================================================
+<===> calc_unsafe_in_binary_operator/input.scss
+// Regression test for sass/dart-sass#2523
+b {
+  a: round(-(1) + 2);
+}
+
+<===> calc_unsafe_in_binary_operator/output.css
+b {
+  a: 1;
+}
+
+<===> math/slash_as_division/warning
+DEPRECATION WARNING [slash-div]: Using / for division outside of calc() is deprecated and will be removed in Dart Sass 2.0.0.
+
+Recommendation: math.div(2px, round(1.5)) or calc(2px / round(1.5))
+
 More info and automated migrator: https://sass-lang.com/d/slash-div
 
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