test case for css support

__tests__/css.test.tsx

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+import React from 'react';
+import renderer from 'react-test-renderer';
+import { SvgCss, SvgCssUri, inlineStyles } from '../src/css';
+
+test('supports CSS in style element', () => {
+  const xml = `<?xml version="1.0" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg xmlns="http://www.w3.org/2000/svg" version="1.1"
+     width="100%" height="100%" viewBox="0 0 1000 500">
+  <defs>
+    <style type="text/css">
+      /* tag selector */
+      rect {
+        stroke: blue;
+        fill: yellow
+      }
+
+      /* class selector */
+      .redbox { fill: red; }
+
+      /* multiple selectors */
+      g .class-1, g .class-2 {
+        stroke-width: 16
+      }
+
+      /* two classes */
+      .class-2.transparent {
+        fill-opacity: 0.3;
+      }
+
+      /* Commented out
+      rect {
+        fill: black;
+      }
+      */
+    </style>
+  </defs>
+  <g>
+    <rect class="redbox class-1" x="100" y="0" width="1000" height="200" />
+  </g>
+  <g>
+    <rect class="redbox class-2 transparent" x="100" y="350" width="750" height="200" />
+  </g>
+</svg>`;
+
+  const tree = renderer.create(<SvgCss xml={xml} />).toJSON();
+  expect(tree).toMatchSnapshot();
+});