test: add spec for buffer shim

tests/spec/shims/buffer.spec.js

@@ -0,0 +1,23 @@
+'use strict';
+const expect = require('chai').expect;
+const bufferDefault = require('../../../shims/buffer').default;
+const bufferNamed = require('../../../shims/buffer').Buffer;
+const bufferActual = require('../../../src/index').Buffer;
+
+describe.only('path shim', () => {
+  it('default export should be defined', () => {
+    expect(bufferDefault).to.not.be.undefined;
+  });
+
+  it('named export should be defined', () => {
+    expect(bufferNamed).to.not.be.undefined;
+  });
+
+  it('default export should be re-exposing Buffer', () => {
+    expect(bufferDefault).to.equal(bufferActual);
+  });
+
+  it('named export should be re-exposing Buffer', () => {
+    expect(bufferNamed).to.equal(bufferActual);
+  });
+});