MDL-50887 antivirus: Add unit tests for manager class.

To run just this test, use:
vendor/bin/phpunit core_antivirus_testcase lib/tests/antivirus_test.php

lib/tests/antivirus_test.php

@@ -0,0 +1,37 @@
+<?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 antivirus manager.
+ *
+ * @package    core_antivirus
+ * @category   phpunit
+ * @copyright  2016 Ruslan Kabalin, Lancaster University.
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+class core_antivirus_testcase extends advanced_testcase {
+
+    public function test_manager_get_antivirus() {
+        // We are using clamav plugin in the test,
+        // as the only plugin we know exists for sure.
+        $antivirusviaget = \core\antivirus\manager::get_antivirus('clamav');
+        $antivirusdirect = new \antivirus_clamav\scanner();
+        $this->assertEquals($antivirusdirect, $antivirusviaget);
+    }
+}