diff --git a/tests/externallib_test.php b/tests/externallib_test.php
new file mode 100644
index 0000000..e44dcb6
--- /dev/null
+++ b/tests/externallib_test.php
@@ -0,0 +1,143 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Tests for externallib.php.
+ *
+ * @package    auth_userkey
+ * @copyright  2016 Dmitrii Metelkin (dmitriim@catalyst-au.net)
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+
+class auth_userkey_externallib_testcase extends advanced_testcase {
+    /**
+     * User object.
+     *
+     * @var
+     */
+    protected $user = array();
+
+    /**
+     * Initial set up.
+     */
+    public function setUp() {
+        global $CFG;
+
+        require_once($CFG->libdir . "/externallib.php");
+        require_once($CFG->dirroot . '/auth/userkey/externallib.php');
+
+        $this->resetAfterTest();
+
+        $this->setAdminUser();
+
+        $user = array();
+        $user['username'] = 'username';
+        $user['email'] = 'exists@test.com';
+        $user['idnumber'] = 'idnumber';
+        $this->user = self::getDataGenerator()->create_user($user);
+    }
+
+    /**
+     * Test successful web service calls.
+     */
+    public function test_successful_webservice_calls() {
+        global $DB, $CFG;
+
+        // Email.
+        $params = array(
+            'email' => 'exists@test.com',
+        );
+
+        // Simulate the web service server.
+        $result = auth_userkey_external::request_login_url($params);
+        $result = external_api::clean_returnvalue(auth_userkey_external::request_login_url_returns(), $result);
+
+        $actualkey = $DB->get_record('user_private_key', array('userid' => $this->user->id));
+        $expectedurl = $CFG->wwwroot . '/auth/userkey/login.php?key=' . $actualkey->value;
+
+        $this->assertTrue(is_array($result));
+        $this->assertTrue(key_exists('loginurl', $result));
+        $this->assertEquals($expectedurl, $result['loginurl']);
+
+        // Username.
+        set_config('mappingfield', 'username', 'auth_userkey');
+        $params = array(
+            'username' => 'username',
+        );
+
+        // Simulate the web service server.
+        $result = auth_userkey_external::request_login_url($params);
+        $result = external_api::clean_returnvalue(auth_userkey_external::request_login_url_returns(), $result);
+
+        $actualkey = $DB->get_record('user_private_key', array('userid' => $this->user->id));
+        $expectedurl = $CFG->wwwroot . '/auth/userkey/login.php?key=' . $actualkey->value;
+
+        $this->assertTrue(is_array($result));
+        $this->assertTrue(key_exists('loginurl', $result));
+        $this->assertEquals($expectedurl, $result['loginurl']);
+
+        // Idnumber.
+        set_config('mappingfield', 'idnumber', 'auth_userkey');
+        $params = array(
+            'idnumber' => 'idnumber',
+        );
+
+        // Simulate the web service server.
+        $result = auth_userkey_external::request_login_url($params);
+        $result = external_api::clean_returnvalue(auth_userkey_external::request_login_url_returns(), $result);
+
+        $actualkey = $DB->get_record('user_private_key', array('userid' => $this->user->id));
+        $expectedurl = $CFG->wwwroot . '/auth/userkey/login.php?key=' . $actualkey->value;
+
+        $this->assertTrue(is_array($result));
+        $this->assertTrue(key_exists('loginurl', $result));
+        $this->assertEquals($expectedurl, $result['loginurl']);
+    }
+
+    /**
+     * Test call with incorrect required parameter.
+     *
+     * @expectedException invalid_parameter_exception
+     * @expectedExceptionMessage Invalid parameter value detected (Required field "email" is not set or empty.)
+     */
+    public function test_request_incorrect_parameters() {
+        $params = array(
+            'bla' => 'exists@test.com',
+        );
+        // Simulate the web service server.
+        $result = auth_userkey_external::request_login_url($params);
+        $result = external_api::clean_returnvalue(auth_userkey_external::request_login_url_returns(), $result);
+    }
+
+    /**
+     * Test request for a user who is not exist.
+     *
+     * @expectedException invalid_parameter_exception
+     * @expectedExceptionMessage Invalid parameter value detected (User is not exist)
+     */
+    public function test_request_not_existing_user() {
+        $params = array(
+            'email' => 'notexists@test.com',
+        );
+
+        // Simulate the web service server.
+        $result = auth_userkey_external::request_login_url($params);
+        $result = external_api::clean_returnvalue(auth_userkey_external::request_login_url_returns(), $result);
+    }
+}