diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..7e0764d
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,29 @@
+name: Test
+on: [push, pull_request]
+jobs:
+  test:
+    name: Test PHP ${{ matrix.php-version }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php-version: ['8.0', '8.1', '8.2', '8.3', '8.4']
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ matrix.php-version }}
+    - name: PHP Version
+      run: php --version
+    - name: Composer Version
+      run: composer --version
+    - name: Install Dependencies
+      run: COMPOSER_MEMORY_LIMIT=-1 composer install
+    - name: Run Tests
+      run: vendor/bin/phpunit --coverage-clover ./coverage.xml
+    - name: Upload Coverage
+      if: ${{ matrix.php-version == '8.2' }}
+      uses: codecov/codecov-action@v1
+      with:
+        file: ./coverage.xml
diff --git a/.gitignore b/.gitignore
index c422267..a2144a3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,4 @@
+composer.lock
 composer.phar
+.phpunit.result.cache
 /vendor/
-
-# Commit your application's lock file http://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file
-# You may choose to ignore a library lock file http://getcomposer.org/doc/02-libraries.md#lock-file
-# composer.lock
diff --git a/LICENSE b/LICENSE
index 9ccb0e7..ab5ad02 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2016 Josh Sherman
+Copyright (c) 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023 Gravity Boulevard, LLC
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/README.md b/README.md
index 6a07365..81a1456 100644
--- a/README.md
+++ b/README.md
@@ -1,30 +1,266 @@
-# php-holidayapi
-Official PHP library for [Holiday API](https://holidayapi.com)
+# Holiday API PHP Library
+
+[![License](https://img.shields.io/packagist/l/holidayapi/holidayapi-php?style=for-the-badge)](https://github.com/holidayapi/holidayapi-php/blob/master/LICENSE)
+![PHP Version](https://img.shields.io/packagist/php-v/holidayapi/holidayapi-php?style=for-the-badge)
+[![Code Coverage](https://img.shields.io/codecov/c/github/holidayapi/holidayapi-php?style=for-the-badge)](https://codecov.io/gh/holidayapi/holidayapi-php)
+
+Official PHP library for [Holiday API](https://holidayapi.com) providing quick
+and easy access to holiday information from applications written in PHP.
+
+## Documentation
+
+Full documentation of the Holiday API endpoints is available
+[here](https://holidayapi.com/docs).
 
 ## Installation
 
 ```shell
-composer require "joshtronic/php-holidayapi:dev-master"
+composer require holidayapi/holidayapi-php
 ```
 
 ## Usage
 
 ```php
-$hapi = new HolidayAPI\v1('_YOUR_API_KEY_');
+<?php
+$key = 'Insert your API key here';
+$holiday_api = new \HolidayAPI\Client(['key' => $key]);
 
-$parameters = array(
-  // Required
-  'country' => 'US',
-  'year'    => 2016,
-  // Optional
-  // 'month'    => 7,
-  // 'day'      => 4,
-  // 'previous' => true,
-  // 'upcoming' => true,
-  // 'public'   => true,
-  // 'pretty'   => true,
-);
+try {
+    // Fetch supported countries and subdivisions
+    $countries = $holiday_api->countries();
 
-$response = $hapi->holidays($parameters);
+    // Fetch supported languages
+    $languages = $holiday_api->languages();
+
+    // Fetch holidays with minimum parameters
+    $holidays = $holiday_api->holidays([
+      'country' => 'US',
+      'year' => 2019,
+    ]);
+
+    var_dump($countries, $languages, $holidays);
+} catch (Exception $e) {
+    var_dump($e);
+}
 ```
 
+## Examples
+
+### Countries
+
+#### Fetch all supported countries
+
+```php
+<?php
+$holiday_api->countries();
+```
+
+#### Fetch only countries with public holidays
+
+```php
+<?php
+$holiday_api->countries([
+  'public' => true,
+]);
+```
+
+#### Fetch a supported country by code
+
+```php
+<?php
+$holiday_api->countries([
+  'country' => 'NO',
+]);
+```
+
+#### Search for countries by code or name
+
+```php
+<?php
+$holiday_api->countries([
+  'search' => 'united',
+]);
+```
+
+### Languages
+
+#### Fetch all supported languages
+
+```php
+<?php
+$holiday_api->languages();
+```
+
+#### Fetch a supported language by code
+
+```php
+<?php
+$holiday_api->languages([
+  'language' => 'es',
+]);
+```
+
+#### Search for languages by code or name
+
+```php
+<?php
+$holiday_api->languages([
+  'search' => 'Chinese',
+]);
+```
+
+### Holidays
+
+#### Fetch holidays for a specific year
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+]);
+```
+
+#### Fetch holidays for a specific month
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'month' => 7,
+]);
+```
+
+#### Fetch holidays for a specific day
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'month' => 7,
+  'day' => 4,
+]);
+```
+
+#### Fetch upcoming holidays based on a specific date
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'month' => 7,
+  'day' => 4,
+  'upcoming' => true,
+]);
+```
+
+#### Fetch previous holidays based on a specific date
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'month' => 7,
+  'day' => 4,
+  'previous' => true,
+]);
+```
+
+#### Fetch only public holidays
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'public' => true,
+]);
+```
+
+#### Fetch holidays for a specific subdivision
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'GB-ENG',
+  'year' => 2019,
+]);
+```
+
+#### Include subdivision holidays with countrywide holidays
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'subdivisions' => true,
+]);
+```
+
+#### Search for a holiday by name
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'search' => 'New Year',
+]);
+```
+
+#### Translate holidays to another language
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US',
+  'year' => 2019,
+  'language' => 'zh', // Chinese (Simplified)
+]);
+```
+
+#### Fetch holidays for multiple countries
+
+```php
+<?php
+$holiday_api->holidays([
+  'country' => 'US,GB,NZ',
+  'year' => 2019,
+]);
+
+$holiday_api->holidays([
+  'country' => ['US', 'GB', 'NZ'],
+  'year' => 2019,
+]);
+```
+
+### Workday
+
+#### Fetch workday 7 business days after a date
+
+```php
+<?php
+$holiday_api->workday([
+  'country' => 'US',
+  'start' => '2019-07-01',
+  'days' => 7,
+]);
+```
+
+### Workdays
+
+#### Fetch number of workdays between two dates
+
+```php
+<?php
+$holiday_api->workdays([
+  'country' => 'US',
+  'start' => '2019-07-01',
+  'end' => '2019-07-10',
+]);
+```
diff --git a/codecov.yml b/codecov.yml
new file mode 100644
index 0000000..657d8f7
--- /dev/null
+++ b/codecov.yml
@@ -0,0 +1,20 @@
+codecov:
+  require_ci_to_pass: yes
+
+coverage:
+  precision: 2
+  round: down
+  range: "70...100"
+
+parsers:
+  gcov:
+    branch_detection:
+      conditional: yes
+      loop: yes
+      method: no
+      macro: no
+
+comment:
+  layout: "reach,diff,flags,tree"
+  behavior: default
+  require_changes: no
diff --git a/composer.json b/composer.json
index 78f9a03..3129ca8 100644
--- a/composer.json
+++ b/composer.json
@@ -1,23 +1,37 @@
 {
-    "name": "joshtronic/php-holidayapi",
-    "description": "Official PHP library for Holiday API",
-    "version": "1.0.0",
-    "type": "library",
-    "keywords": [ "holiday", "holidays", "holidayapi" ],
-    "homepage": "https://github.com/joshtronic/php-holidayapi",
-    "license": "MIT",
-    "authors": [{
-        "name": "Josh Sherman",
-        "email": "hello@holidayapi.com",
-        "homepage": "https://holidayapi.com,"
-    }],
-    "require": {
-        "php": ">=5.3.0"
-    },
-    "require-dev": {
-        "satooshi/php-coveralls": "~1.0"
-    },
-    "autoload": {
-        "psr-4": { "HolidayAPI\\": "src/" }
+  "name": "holidayapi/holidayapi-php",
+  "description": "Official PHP library for Holiday API",
+  "version": "4.0.0",
+  "type": "library",
+  "keywords": [
+    "calendar",
+    "holiday",
+    "holidays",
+    "holidayapi"
+  ],
+  "homepage": "https://github.com/holidayapi/holidayapi-php",
+  "license": "MIT",
+  "authors": [{
+    "name": "Josh Sherman",
+    "email": "hello@holidayapi.com",
+    "homepage": "https://holidayapi.com"
+  }],
+  "require": {
+    "php": ">=8.0",
+    "ext-json": "*",
+    "ext-curl": "*"
+  },
+  "require-dev": {
+    "phpunit/phpunit": "^9.0"
+  },
+  "autoload": {
+    "psr-4": {
+      "HolidayAPI\\": "src/"
     }
+  },
+  "autoload-dev": {
+    "psr-4": {
+      "HolidayAPI\\Tests\\": "tests/"
+    }
+  }
 }
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..92f2230
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+  colors="true"
+  bootstrap="./vendor/autoload.php"
+  convertErrorsToExceptions="true"
+  convertNoticesToExceptions="true"
+  convertWarningsToExceptions="true"
+  failOnRisky="true"
+  stopOnError="true"
+  stopOnFailure="true"
+  stopOnIncomplete="true"
+  verbose="true"
+>
+  <testsuites>
+    <testsuite name="Holiday API">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
+  <filter>
+    <whitelist addUncoveredFilesFromWhitelist="true">
+      <directory>./src</directory>
+    </whitelist>
+  </filter>
+</phpunit>
diff --git a/src/Client.php b/src/Client.php
new file mode 100644
index 0000000..0793c97
--- /dev/null
+++ b/src/Client.php
@@ -0,0 +1,85 @@
+<?php
+/**
+ * Copyright (c) Gravity Boulevard, LLC
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+namespace HolidayAPI;
+use HolidayAPI;
+
+class Client
+{
+    private $handler;
+    public $baseUrl;
+    public $key;
+
+    public function __construct($options)
+    {
+        $getYours = 'get yours at HolidayAPI.com';
+        $uuidRegExp = '/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}/';
+
+        if (!isset($options['key'])) {
+            throw new \Exception("Missing API key, {$getYours}");
+        }
+
+        if (!preg_match($uuidRegExp, $options['key'])) {
+            throw new \Exception("Invalid API key, {$getYours}");
+        }
+
+        $version = (isset($options['version']) ? $options['version'] : 1);
+
+        if ($version != 1) {
+            throw new \Exception('Invalid version number, expected "1"');
+        }
+
+        $this->baseUrl = "https://holidayapi.com/v{$version}/";
+        $this->key = $options['key'];
+
+        if (isset($options['handler'])) {
+            $this->handler = $options['handler'];
+        } else {
+            $this->handler = new Request();
+        }
+    }
+
+    private function createUrl($endpoint, $request = array())
+    {
+        $parameters = array_merge(array('key' => $this->key), $request);
+        $parameters = http_build_query($parameters);
+
+        return "{$this->baseUrl}{$endpoint}?{$parameters}";
+    }
+
+    private function request($endpoint, $request)
+    {
+        return $this->handler->get($this->createUrl($endpoint, $request));
+    }
+
+    public function countries($request = array())
+    {
+        return $this->request('countries', $request);
+    }
+
+    public function holidays($request)
+    {
+        return $this->request('holidays', $request);
+    }
+
+    public function languages($request = array())
+    {
+        return $this->request('languages', $request);
+    }
+
+    public function workday($request)
+    {
+        return $this->request('workday', $request);
+    }
+
+    public function workdays($request)
+    {
+        return $this->request('workdays', $request);
+    }
+}
+
diff --git a/src/Request.php b/src/Request.php
new file mode 100644
index 0000000..355e69a
--- /dev/null
+++ b/src/Request.php
@@ -0,0 +1,79 @@
+<?php
+/**
+ * Copyright (c) Gravity Boulevard, LLC
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+namespace HolidayAPI;
+
+class Request
+{
+    private $handlers = array();
+
+    public function __construct($handlers = array())
+    {
+        $this->handlers = $handlers;
+    }
+
+    public function execute($curl)
+    {
+        if (isset($this->handlers['execute'])) {
+            $info = curl_getinfo($curl);
+            $url = $info['url'];
+
+            if (isset($this->handlers['execute'][$url])) {
+                return $this->handlers['execute'][$url]($curl);
+            }
+        }
+
+        return curl_exec($curl);
+    }
+
+    public function error($curl)
+    {
+        if (isset($this->handlers['error'])) {
+            $info = curl_getinfo($curl);
+            $url = $info['url'];
+
+            if (isset($this->handlers['error'][$url])) {
+                return $this->handlers['error'][$url]($curl);
+            }
+        }
+
+        return curl_error($curl);
+    }
+
+    public function get($url)
+    {
+        $curl = curl_init();
+
+        curl_setopt_array($curl, array(
+            CURLOPT_URL => $url,
+            CURLOPT_HEADER => false,
+            CURLOPT_SSL_VERIFYPEER => true,
+            CURLOPT_RETURNTRANSFER => true,
+        ));
+
+        $response = $this->execute($curl);
+
+        if ($error = $this->error($curl)) {
+            throw new \Exception($error);
+        }
+
+        curl_close($curl);
+        $response = json_decode($response, true);
+
+        if (!$response) {
+            throw new \Exception('Empty response received');
+        }
+
+        if (isset($response['error'])) {
+            throw new \Exception($response['error'], $response['status']);
+        }
+
+        return $response;
+    }
+}
+
diff --git a/src/v1.php b/src/v1.php
deleted file mode 100644
index 472bd62..0000000
--- a/src/v1.php
+++ /dev/null
@@ -1,51 +0,0 @@
-<?php
-namespace HolidayAPI;
-
-class v1
-{
-    private $parameters = array();
-
-    public function __set($variable, $value)
-    {
-        $this->parameters[$variable] = $value;
-    }
-
-    public function __construct($key = null)
-    {
-        if ($key) {
-            $this->key = $key;
-        }
-    }
-
-    public function holidays($parameters = array())
-    {
-        $parameters = array_merge($this->parameters, $parameters);
-        $parameters = http_build_query($parameters);
-
-        $url  = 'https://holidayapi.com/v1/holidays?' . $parameters;
-        $curl = curl_init();
-
-        curl_setopt_array($curl, array(
-            CURLOPT_URL            => $url,
-            CURLOPT_HEADER         => false,
-            CURLOPT_SSL_VERIFYPEER => true,
-            CURLOPT_RETURNTRANSFER => true,
-        ));
-
-        $response = curl_exec($curl);
-
-        if ($error = curl_error($curl)) {
-            return false;
-        }
-
-        curl_close($curl);
-        $response = json_decode($response, true);
-
-        if (!$response) {
-            return false;
-        }
-
-        return $response;
-    }
-}
-
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
new file mode 100644
index 0000000..14f83c7
--- /dev/null
+++ b/tests/ClientTest.php
@@ -0,0 +1,539 @@
+<?php
+namespace HolidayAPI\Tests;
+use HolidayAPI\Client;
+use HolidayAPI\Request;
+use PHPUnit\Framework\TestCase;
+
+class ClientTest extends TestCase
+{
+    const BASE_URL = 'https://holidayapi.com/v1/';
+    const KEY = '8e4de28c-4b18-49f0-9aba-0bd6b424fc38';
+
+    public function testMissingKey()
+    {
+        if (version_compare(PHP_VERSION, '7.3.0', '>=')) {
+            $assertRegExp = 'assertMatchesRegularExpression';
+        } else {
+            $assertRegExp = 'assertRegExp';
+        }
+
+        try {
+            new Client(array());
+        } catch (\Exception $e) {
+            $this->$assertRegExp('/missing api key/i', $e->getMessage());
+        }
+    }
+
+    public function testInvalidKey()
+    {
+        if (version_compare(PHP_VERSION, '7.3.0', '>=')) {
+            $assertRegExp = 'assertMatchesRegularExpression';
+        } else {
+            $assertRegExp = 'assertRegExp';
+        }
+
+        try {
+            new Client(array(
+                'key' => 'zzzzzzzz-zzzz-zzzz-zzzz-zzzzzzzzzzzz',
+            ));
+        } catch (\Exception $e) {
+            $this->$assertRegExp('/invalid api key/i', $e->getMessage());
+        }
+    }
+
+    public function testVersionTooLow()
+    {
+        if (version_compare(PHP_VERSION, '7.3.0', '>=')) {
+            $assertRegExp = 'assertMatchesRegularExpression';
+        } else {
+            $assertRegExp = 'assertRegExp';
+        }
+
+        try {
+            new Client(array('key' => self::KEY, 'version' => 0));
+        } catch (\Exception $e) {
+            $this->$assertRegExp('/invalid version/i', $e->getMessage());
+        }
+    }
+
+    public function testVersionTooHigh()
+    {
+        if (version_compare(PHP_VERSION, '7.3.0', '>=')) {
+            $assertRegExp = 'assertMatchesRegularExpression';
+        } else {
+            $assertRegExp = 'assertRegExp';
+        }
+
+        try {
+            new Client(array('key' => self::KEY, 'version' => 2));
+        } catch (\Exception $e) {
+            $this->$assertRegExp('/invalid version/i', $e->getMessage());
+        }
+    }
+
+    public function testAssignClassMembers()
+    {
+        $client = new Client(array('key' => self::KEY));
+
+        $this->assertSame(self::BASE_URL, $client->baseUrl);
+        $this->assertSame(self::KEY, $client->key);
+    }
+
+    public function testReturnCountries()
+    {
+        $url = self::BASE_URL . 'countries?key=' . self::KEY;
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 200,
+                        'countries' => array(
+                            array(
+                                'code' => 'ST',
+                                'name' => 'Sao Tome and Principle',
+                            ),
+                        ),
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        $this->assertEquals(array(
+            'status' => 200,
+            'countries' => array(
+                array(
+                    'code' => 'ST',
+                    'name' => 'Sao Tome and Principle',
+                ),
+            ),
+        ), $client->countries());
+    }
+
+    public function testCountriesRaise4xxErrors()
+    {
+        $url = self::BASE_URL . 'countries?key=' . self::KEY;
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 429,
+                        'error' => 'Rate limit exceeded',
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->countries();
+        } catch (\Exception $e) {
+            $this->assertSame(429, $e->getCode());
+            $this->assertSame('Rate limit exceeded', $e->getMessage());
+        }
+    }
+
+    public function testCountriesRaise5xxErrors()
+    {
+        $url = self::BASE_URL . 'countries?key=' . self::KEY;
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return false;
+                },
+            ),
+            'error' => array(
+                $url => function ()
+                {
+                    return 'Internal server error';
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->countries();
+        } catch (\Exception $e) {
+            $this->assertSame('Internal server error', $e->getMessage());
+        }
+    }
+
+    public function testReturnHolidays()
+    {
+        $url = self::BASE_URL . 'holidays?key=' . self::KEY . '&country=US&year=2015&month=7&day=4';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 200,
+                        'holidays' => array(
+                            array(
+                                'name' => 'Independence Day',
+                                'date' => '2015-07-04',
+                                'observed' => '2015-07-03',
+                                'public' => true,
+                            ),
+                        ),
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        $this->assertEquals(array(
+            'status' => 200,
+            'holidays' => array(
+                array(
+                    'name' => 'Independence Day',
+                    'date' => '2015-07-04',
+                    'observed' => '2015-07-03',
+                    'public' => true,
+                ),
+            ),
+        ), $client->holidays(array(
+            'country' => 'US',
+            'year' => 2015,
+            'month' => 7,
+            'day' => 4,
+        )));
+    }
+
+    public function testHolidaysRaise4xxErrors()
+    {
+        $url = self::BASE_URL . 'holidays?key=' . self::KEY . '&country=US&year=2019';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 429,
+                        'error' => 'Rate limit exceeded',
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->holidays(array('country' => 'US', 'year' => 2019));
+        } catch (\Exception $e) {
+            $this->assertSame(429, $e->getCode());
+            $this->assertSame('Rate limit exceeded', $e->getMessage());
+        }
+    }
+
+    public function testHolidaysRaise5xxErrors()
+    {
+        $url = self::BASE_URL . 'holidays?key=' . self::KEY . '&country=US&year=2019';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return false;
+                },
+            ),
+            'error' => array(
+                $url => function ()
+                {
+                    return 'Internal server error';
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->holidays(array('country' => 'US', 'year' => 2019));
+        } catch (\Exception $e) {
+            $this->assertSame('Internal server error', $e->getMessage());
+        }
+    }
+
+    public function testReturnLanguages()
+    {
+        $url = self::BASE_URL . 'languages?key=' . self::KEY;
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 200,
+                        'languages' => array(
+                            array(
+                                'code' => 'en',
+                                'name' => 'English',
+                            ),
+                        ),
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        $this->assertEquals(array(
+            'status' => 200,
+            'languages' => array(
+                array(
+                    'code' => 'en',
+                    'name' => 'English',
+                ),
+            ),
+        ), $client->languages());
+    }
+
+    public function testLanguagesRaise4xxErrors()
+    {
+        $url = self::BASE_URL . 'languages?key=' . self::KEY;
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 429,
+                        'error' => 'Rate limit exceeded',
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->languages();
+        } catch (\Exception $e) {
+            $this->assertSame(429, $e->getCode());
+            $this->assertSame('Rate limit exceeded', $e->getMessage());
+        }
+    }
+
+    public function testLanguagesRaise5xxErrors()
+    {
+        $url = self::BASE_URL . 'languages?key=' . self::KEY;
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return false;
+                },
+            ),
+            'error' => array(
+                $url => function ()
+                {
+                    return 'Internal server error';
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->languages();
+        } catch (\Exception $e) {
+            $this->assertSame('Internal server error', $e->getMessage());
+        }
+    }
+
+    public function testReturnWorkday()
+    {
+        $url = self::BASE_URL . 'workday?key=' . self::KEY . '&country=US&start=2019-07-01&days=10';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 200,
+                        'workday' => array(
+                            'date' => '2019-07-16',
+                        ),
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        $this->assertEquals(array(
+            'status' => 200,
+            'workday' => array(
+                'date' => '2019-07-16',
+            ),
+        ), $client->workday(array(
+            'country' => 'US',
+            'start' => '2019-07-01',
+            'days' => 10,
+        )));
+    }
+
+    public function testWorkdayRaise4xxErrors()
+    {
+        $url = self::BASE_URL . 'workday?key=' . self::KEY . '&country=US&start=2019-07-01&days=10';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 429,
+                        'error' => 'Rate limit exceeded',
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->workday(array(
+                'country' => 'US',
+                'start' => '2019-07-01',
+                'days' => 10,
+            ));
+        } catch (\Exception $e) {
+            $this->assertSame(429, $e->getCode());
+            $this->assertSame('Rate limit exceeded', $e->getMessage());
+        }
+    }
+
+    public function testWorkdayRaise5xxErrors()
+    {
+        $url = self::BASE_URL . 'workday?key=' . self::KEY . '&country=US&start=2019-07-01&days=10';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return false;
+                },
+            ),
+            'error' => array(
+                $url => function ()
+                {
+                    return 'Internal server error';
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->workday(array(
+                'country' => 'US',
+                'start' => '2019-07-01',
+                'days' => 10,
+            ));
+        } catch (\Exception $e) {
+            $this->assertSame('Internal server error', $e->getMessage());
+        }
+    }
+
+    public function testReturnWorkdays()
+    {
+        $url = self::BASE_URL . 'workdays?key=' . self::KEY . '&country=US&start=2019-07-01&end=2019-07-10';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 200,
+                        'workdays' => 7,
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        $this->assertEquals(array(
+            'status' => 200,
+            'workdays' => 7,
+        ), $client->workdays(array(
+            'country' => 'US',
+            'start' => '2019-07-01',
+            'end' => '2019-07-10',
+        )));
+    }
+
+    public function testWorkdaysRaise4xxErrors()
+    {
+        $url = self::BASE_URL . 'workdays?key=' . self::KEY . '&country=US&start=2019-07-01&end=2019-07-10';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 429,
+                        'error' => 'Rate limit exceeded',
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->workdays(array(
+                'country' => 'US',
+                'start' => '2019-07-01',
+                'end' => '2019-07-10',
+            ));
+        } catch (\Exception $e) {
+            $this->assertSame(429, $e->getCode());
+            $this->assertSame('Rate limit exceeded', $e->getMessage());
+        }
+    }
+
+    public function testWorkdaysRaise5xxErrors()
+    {
+        $url = self::BASE_URL . 'workdays?key=' . self::KEY . '&country=US&start=2019-07-01&end=2019-07-10';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return false;
+                },
+            ),
+            'error' => array(
+                $url => function ()
+                {
+                    return 'Internal server error';
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        try {
+            $client->workdays(array(
+                'country' => 'US',
+                'start' => '2019-07-01',
+                'end' => '2019-07-10',
+            ));
+        } catch (\Exception $e) {
+            $this->assertSame('Internal server error', $e->getMessage());
+        }
+    }
+}
+
diff --git a/tests/RequestTest.php b/tests/RequestTest.php
new file mode 100644
index 0000000..f42776d
--- /dev/null
+++ b/tests/RequestTest.php
@@ -0,0 +1,42 @@
+<?php
+namespace HolidayAPI\Tests;
+use HolidayAPI\Request;
+use PHPUnit\Framework\TestCase;
+
+class RequestTest extends TestCase
+{
+    public function testExecute()
+    {
+        $curl = curl_init();
+        $request = new Request();
+
+        $this->assertFalse($request->execute($curl));
+    }
+
+    public function testGet()
+    {
+        if (version_compare(PHP_VERSION, '7.3.0', '>=')) {
+            $assertRegExp = 'assertMatchesRegularExpression';
+        } else {
+            $assertRegExp = 'assertRegExp';
+        }
+
+        $url = 'https://holidayapi.com';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return '';
+                },
+            ),
+        ));
+
+        try {
+            $request->get($url);
+        } catch (\Exception $e) {
+            $this->$assertRegExp('/empty response/i', $e->getMessage());
+        }
+    }
+}
+