add common HTTP errors

libraries/o-error/test/http.test.js

@@ -0,0 +1,20 @@
+const OError = require('..')
+const HttpErrors = require('../http')
+
+describe('OError/http', () => {
+  it('is instance of OError', () => {
+    try {
+      throw new HttpErrors.ConflictError()
+    } catch (e) {
+      expect(e).to.be.instanceof(OError)
+    }
+  })
+
+  it('has status code', () => {
+    try {
+      throw new HttpErrors.ConflictError()
+    } catch (e) {
+      expect(e.statusCode).to.equal(409)
+    }
+  })
+})