test: add inital tests

Author: ntwb

__tests__/__snapshots__/index.test.js.snap

@@ -0,0 +1,16 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`it contains expected keys 1`] = `
+Array [
+  "clearMocks",
+  "collectCoverage",
+  "coverageDirectory",
+  "coverageReporters",
+  "coverageThreshold",
+  "moduleFileExtensions",
+  "setupFiles",
+  "testEnvironment",
+  "testMatch",
+  "verbose",
+]
+`;

__tests__/index.test.js

@@ -0,0 +1,6 @@
+"use strict"
+
+const preset = require("../jest-preset.json");
+test('it contains expected keys', () => {
+  expect(Object.keys(preset)).toMatchSnapshot();
+});