Add basic wrapping test

packages/block-editor/src/utils/test/transform-styles.js

@@ -0,0 +1,19 @@
+/**
+ * Internal dependencies
+ */
+import transformStyles from '../transform-styles';
+
+it( 'should wrap selectors inside container queries', () => {
+	const input = `
+	@container (width > 400px) {
+		  h1 { color: red; }
+	}`;
+	const output = transformStyles( { input: { css: input } }, 'my-namespace' );
+
+	expect( output ).toEqual( [
+		`
+	@container (width > 400px) {
+		  .my-namespace h1 { color: red; }
+	}`,
+	] );
+} );