fix(coverage): support webpack sourcemaps format

lib/coverage.js

@@ -133,9 +133,9 @@ const Coverage = module.exports = inherit({
             return;
         }
 
-        var base64Prefix = 'data:application/json;base64,';
-        if (_.includes(sourceMapUrl, base64Prefix)) {
-            var base64Str = sourceMapUrl.split(base64Prefix)[1],
+        var base64Prefix = /^data:application\/json;(?:charset=utf-8;)?base64,/;
+        if (base64Prefix.test(sourceMapUrl)) {
+            var base64Str = sourceMapUrl.replace(base64Prefix, ''),
                 sourceMapStr = new Buffer(base64Str, 'base64').toString('utf8');
             return new SourceMapConsumer(JSON.parse(sourceMapStr));
         }

test/unit/coverage.js

@@ -49,4 +49,42 @@ describe('coverage', () => {
             assert.deepEqual(coverage.byURL['http://some/url'].coverage, {'.some-selector': 'full'});
         });
     });
+
+    describe('getSourceMap', () => {
+        it('parse source map', () => {
+            const config = createConfig();
+            const coverage = new Coverage(config);
+
+            const ast = {
+                stylesheet: {
+                    rules: [{
+                        type: 'comment',
+                        comment: '# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IiIsImZpbGUiOiJzdHlsZXMuY3NzIiwic291cmNlUm9vdCI6IiJ9'
+                    }]
+                }
+            };
+
+            const map = coverage.getSourceMap(ast, '', '');
+
+            assert.equal(map.file, 'styles.css');
+        });
+
+        it('parse webpack source map', () => {
+            const config = createConfig();
+            const coverage = new Coverage(config);
+
+            const ast = {
+                stylesheet: {
+                    rules: [{
+                        type: 'comment',
+                        comment: '# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IiIsImZpbGUiOiJzdHlsZXMuY3NzIiwic291cmNlUm9vdCI6IiJ9'
+                    }]
+                }
+            };
+
+            const map = coverage.getSourceMap(ast, '', '');
+
+            assert.equal(map.file, 'styles.css');
+        });
+    });
 });