fix: Illegal constructor

Author: eps1lon

test/utils/initMatchers.js

@@ -104,7 +104,12 @@ chai.use((chaiAPI, utils) => {
      * @returns {CSSStyleDeclaration}
      */
     function pretendVisibleGetComputedStyle(element) {
-      const declaration = new CSSStyleDeclaration();
+      // `CSSStyleDeclaration` is not constructable
+      // https://stackoverflow.com/a/52732909/3406963
+      // this is not equivalent to the declaration from `getComputedStyle`
+      // e.g `getComputedStyle` would return a readonly declaration
+      // let's hope this doesn't get passed around until it's no longer clear where it comes from
+      const declaration = document.createElement('span').style;
 
       // initial values
       declaration.content = '';