diff --git a/step/email/tests/lib_test.php b/step/email/tests/lib_test.php
new file mode 100644
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--- /dev/null
+++ b/step/email/tests/lib_test.php
@@ -0,0 +1,58 @@
+<?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/>.
+/**
+ * Unit tests for the lifecyclestep_email lib.php.
+ *
+ * @package    lifecyclestep_email
+ * @copyright  2024 Justus Dieckmann, University of Münster.
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+namespace lifecyclestep_email;
+
+/**
+ * Unit tests for the lifecyclestep_email lib.php.
+ *
+ * @package    lifecyclestep_email
+ * @copyright  2024 Justus Dieckmann, University of Münster.
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+final class lib_test extends \advanced_testcase {
+
+    /**
+     * Tests \tool_lifecycle\step\email::replace_placeholders.
+     *
+     * @covers \tool_lifecycle\step\email::replace_placeholders
+     */
+    public function test_replace_placeholders(): void {
+        $this->resetAfterTest();
+
+        $user1 = $this->getDataGenerator()->create_user(['firstname' => 'Jane', 'lastname' => 'Doe']);
+        $course1 = $this->getDataGenerator()->create_course(['fullname' => 'Course 1', 'shortname' => 'C1']);
+        $course2 = $this->getDataGenerator()->create_course(['fullname' => 'Course 2', 'shortname' => 'C2']);
+        $lib = new \tool_lifecycle\step\email();
+        $callReplacePlaceholders = function($strings, $user, $stepid, $mailentries) {
+            return $this->replace_placeholders($strings, $user, $stepid, $mailentries);
+        };
+        $response = $callReplacePlaceholders->call($lib, [
+                "##firstname##\n##lastname##\n##courses##\n##shortcourses##",
+                "##firstname##<br>##lastname##<br>##courses-html##<br>##shortcourses-html##"
+        ], $user1, 0, [(object) ['courseid' => $course1->id], (object) ['courseid' => $course2->id]]);
+
+        $this->assertCount(2, $response);
+        $this->assertEquals("Jane\nDoe\nCourse 1\nCourse 2\nC1\nC2", $response[0]);
+        $this->assertEquals("Jane<br>Doe<br>Course 1<br>Course 2<br>C1<br>C2", $response[1]);
+    }
+}