@@ -1,13 +1,16 @@
 src_files := src/*.js
 src_dir   := src
 
-.PHONY: all lint build
+.PHONY: all lint test build
 
-all: lint build
+all: lint test build
 
 lint: dist/icons.json
 	./node_modules/.bin/eslint .
 
+test:
+	./node_modules/.bin/jest
+
 build: dist/feather.js dist/feather.min.js dist/icons
 
 node_modules:
 
@@ -0,0 +1,26 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`processes SVG correctly 1`] = `
+"<svg
+  xmlns=\\"http://www.w3.org/2000/svg\\"
+  width=\\"24\\"
+  height=\\"24\\"
+  viewBox=\\"0 0 24 24\\"
+  fill=\\"none\\"
+  stroke=\\"currentColor\\"
+  stroke-width=\\"2\\"
+  stroke-linecap=\\"round\\"
+  stroke-linejoin=\\"round\\"
+>
+  <line x1=\\"23\\" y1=\\"1\\" x2=\\"1\\" y2=\\"23\\" />
+  <line x1=\\"1\\" y1=\\"1\\" x2=\\"23\\" y2=\\"23\\" />
+</svg>
+"
+`;
+
+exports[`rejects when passed unparsable SVG string 1`] = `
+[Error: Error in parsing SVG: Unclosed root tag
+Line: 0
+Column: 10
+Char: ]
+`;
@@ -0,0 +1,15 @@
+/* eslint-env jest */
+import processSvg from '../process-svg';
+
+test('processes SVG correctly', () => {
+  const SVG =
+    '<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24"><title>Title</title><line x1="23" y1="1" x2="1" y2="23" fill="none" stroke="#000" stroke-linecap="round" stroke-linejoin="round" stroke-width="2"/><line x1="1" y1="1" x2="23" y2="23" fill="none" stroke="#000" stroke-linecap="round" stroke-linejoin="round" stroke-width="2"/></svg>';
+
+  expect(processSvg(SVG)).resolves.toMatchSnapshot();
+});
+
+test('rejects when passed unparsable SVG string', () => {
+  const UNPARSABLE_SVG = '<svg></svg';
+
+  expect(processSvg(UNPARSABLE_SVG)).rejects.toMatchSnapshot();
+});
@@ -0,0 +1,59 @@
+/* eslint-disable import/no-extraneous-dependencies */
+import Svgo from 'svgo';
+import cheerio from 'cheerio';
+import { format } from 'prettier';
+
+import DEFAULT_ATTRIBUTES from '../src/default-attributes.json';
+
+/**
+ * Process SVG string.
+ * @param {string} svg - An SVG string.
+ * @param {Promise<string>}
+ */
+function processSvg(svg) {
+  return (
+    optimize(svg)
+      .then(setAttributes)
+      .then(format)
+      // remove semicolon inserted by prettier
+      // because prettier thinks it's formatting JSX not HTML
+      .then(svg => svg.replace(/;/g, ''))
+  );
+}
+
+/**
+ * Optimize SVG with `svgo`.
+ * @param {string} svg - An SVG string.
+ * @returns {Promise<string>}
+ */
+function optimize(svg) {
+  const svgo = new Svgo({
+    plugins: [
+      { convertShapeToPath: false },
+      { mergePaths: false },
+      { removeAttrs: { attrs: '(fill|stroke.*)' } },
+      { removeTitle: true },
+    ],
+  });
+
+  return new Promise(resolve => {
+    svgo.optimize(svg, ({ data }) => resolve(data));
+  });
+}
+
+/**
+ * Set default attibutes on SVG.
+ * @param {string} svg - An SVG string.
+ * @returns {string}
+ */
+function setAttributes(svg) {
+  const $ = cheerio.load(svg);
+
+  Object.keys(DEFAULT_ATTRIBUTES).forEach(key =>
+    $('svg').attr(key, DEFAULT_ATTRIBUTES[key]),
+  );
+
+  return $('body').html();
+}
+
+export default processSvg;
@@ -0,0 +1,15 @@
+/* eslint-disable import/no-extraneous-dependencies */
+import fs from 'fs';
+import path from 'path';
+
+import processSvg from './process-svg';
+
+const ICONS_DIR = path.resolve(__dirname, '../icons');
+
+fs
+  .readdirSync(ICONS_DIR)
+  .filter(file => path.extname(file) === '.svg')
+  .forEach(svgFile => {
+    const svg = fs.readFileSync(path.join(ICONS_DIR, svgFile));
+    processSvg(svg).then(svg => fs.writeFileSync(path.join(ICONS_DIR, svgFile), svg));
+  });