diff --git a/mod/chat/tests/externallib_test.php b/mod/chat/tests/externallib_test.php
index 2443f71d6b1..050753baaa6 100644
--- a/mod/chat/tests/externallib_test.php
+++ b/mod/chat/tests/externallib_test.php
@@ -428,7 +428,8 @@ class mod_chat_external_testcase extends externallib_advanced_testcase {
         $result = external_api::clean_returnvalue(mod_chat_external::get_sessions_returns(), $result);
         $this->assertCount(1, $result['sessions']); // One session.
         $this->assertTrue($result['sessions'][0]['iscomplete']); // Session complete.
-        $this->assertEquals($timenow - HOURSECS + 70, $result['sessions'][0]['sessionstart']);  // First not system message time.
+        // The session started when user1 entered the chat.
+        $this->assertEquals($timenow - HOURSECS, $result['sessions'][0]['sessionstart']);
         $this->assertEmpty($result['warnings']);
     }
 
diff --git a/mod/chat/tests/lib_test.php b/mod/chat/tests/lib_test.php
index 4edef1aea5a..cd9c9e90aec 100644
--- a/mod/chat/tests/lib_test.php
+++ b/mod/chat/tests/lib_test.php
@@ -143,6 +143,201 @@ class mod_chat_lib_testcase extends advanced_testcase {
         $this->assertFalse($actionevent->is_actionable());
     }
 
+    /**
+     * Test for chat_get_sessions().
+     */
+    public function test_chat_get_sessions() {
+        global $DB;
+
+        $this->resetAfterTest();
+
+        $generator = $this->getDataGenerator();
+
+        // Setup test data.
+        $this->setAdminUser();
+        $course = $generator->create_course();
+        $chat = $generator->create_module('chat', ['course' => $course->id]);
+
+        $user1 = $generator->create_user();
+        $user2 = $generator->create_user();
+        $studentrole = $DB->get_record('role', ['shortname' => 'student']);
+        $generator->enrol_user($user1->id, $course->id, $studentrole->id);
+        $generator->enrol_user($user2->id, $course->id, $studentrole->id);
+
+        // Login as user 1.
+        $this->setUser($user1);
+        $chatsid = chat_login_user($chat->id, 'ajax', 0, $course);
+        $chatuser = $DB->get_record('chat_users', ['sid' => $chatsid]);
+
+        // This is when the session starts (when the user enters the chat).
+        $sessionstart = $chatuser->lastping;
+
+        // Send some messages.
+        chat_send_chatmessage($chatuser, 'hello!');
+        chat_send_chatmessage($chatuser, 'bye bye!');
+
+        // Login as user 2.
+        $this->setUser($user2);
+        $chatsid = chat_login_user($chat->id, 'ajax', 0, $course);
+        $chatuser = $DB->get_record('chat_users', ['sid' => $chatsid]);
+
+        // Send a message and take note of this message ID.
+        $messageid = chat_send_chatmessage($chatuser, 'greetings!');
+
+        // This is when the session ends (timestamp of the last message sent to the chat).
+        $sessionend = $DB->get_field('chat_messages', 'timestamp', ['id' => $messageid]);
+
+        // Get the messages for this chat session.
+        $messages = chat_get_session_messages($chat->id, false, 0, 0, 'timestamp DESC');
+
+        // We should have 3 user and 2 system (enter) messages.
+        $this->assertCount(5, $messages);
+
+        // Fetch the chat sessions from the messages we retrieved.
+        $sessions = chat_get_sessions($messages, true);
+
+        // There should be only one session.
+        $this->assertCount(1, $sessions);
+
+        // Get this session.
+        $session = reset($sessions);
+
+        // Confirm that the start and end times of the session matches.
+        $this->assertEquals($sessionstart, $session->sessionstart);
+        $this->assertEquals($sessionend, $session->sessionend);
+        // Confirm we have 2 participants in the chat.
+        $this->assertCount(2, $session->sessionusers);
+    }
+
+    /**
+     * Test for chat_get_sessions with messages belonging to multiple sessions.
+     */
+    public function test_chat_get_sessions_multiple() {
+        $messages = [];
+        $widegap = 5 * 60; // 5 mins.
+        $gap = 5; // 5 secs.
+
+        $now = time();
+        $timestamp = $now;
+
+        // Messages belonging to 3 sessions. Session 1 has 10 messages, 2 has 15, 3 has 25.
+        $sessionusers = [];
+        $sessiontimes = [];
+        $session = 0; // Incomplete session.
+        for ($i = 1; $i <= 50; $i++) {
+            // Take note of expected session times as we go through.
+            switch ($i) {
+                case 1:
+                    // Session 1 start time.
+                    $sessiontimes[0]['start'] = $timestamp;
+                    break;
+                case 10:
+                    // Session 1 end time.
+                    $sessiontimes[0]['end'] = $timestamp;
+                    break;
+                case 11:
+                    // Session 2 start time.
+                    $sessiontimes[1]['start'] = $timestamp;
+                    break;
+                case 25:
+                    // Session 2 end time.
+                    $sessiontimes[1]['end'] = $timestamp;
+                    break;
+                case 26:
+                    // Session 3 start time.
+                    $sessiontimes[2]['start'] = $timestamp;
+                    break;
+                case 50:
+                    // Session 3 end time.
+                    $sessiontimes[2]['end'] = $timestamp;
+                    break;
+            }
+
+            // User 1 to 5.
+            $user = rand(1, 5);
+
+            // Let's also include system messages as well. Give them to pop in 1-in-10 chance.
+            $issystem = rand(1, 10) == 10;
+
+            if ($issystem) {
+                $message = 'enter';
+            } else {
+                $message = 'Message ' . $i;
+                if (!isset($sessionusers[$session][$user])) {
+                    $sessionusers[$session][$user] = 1;
+                } else {
+                    $sessionusers[$session][$user]++;
+                }
+            }
+            $messages[] = (object)[
+                'id' => $i,
+                'chatid' => 1,
+                'userid' => $user,
+                'message' => $message,
+                'issystem' => $issystem,
+                'timestamp' => $timestamp,
+            ];
+
+            // Set the next timestamp.
+            if ($i == 10 || $i == 25) {
+                // New session.
+                $session++;
+                $timestamp += $widegap + 1;
+            } else {
+                $timestamp += $gap;
+            }
+        }
+        // Reverse sort the messages so they're in descending order.
+        rsort($messages);
+
+        // Get chat sessions showing only complete ones.
+        $completesessions = chat_get_sessions($messages);
+        // Session 1 is incomplete, so there should only be 2 sessions when $showall is false.
+        $this->assertCount(2, $completesessions);
+
+        // Reverse sort sessions so they are in ascending order matching our expected session times and users.
+        $completesessions = array_reverse($completesessions);
+        foreach ($completesessions as $index => $session) {
+            // We increment index by 1 because the incomplete expected session (index=0) is not included.
+            $expectedindex = $index + 1;
+
+            // Check the session users.
+            $users = $sessionusers[$expectedindex];
+            $this->assertCount(count($users), $session->sessionusers);
+            // Check the message counts for each user in this session.
+            foreach ($users as $userid => $messagecount) {
+                $this->assertEquals($messagecount, $session->sessionusers[$userid]);
+            }
+
+            $sessionstart = $sessiontimes[$expectedindex]['start'];
+            $sessionend = $sessiontimes[$expectedindex]['end'];
+            $this->assertEquals($sessionstart, $session->sessionstart);
+            $this->assertEquals($sessionend, $session->sessionend);
+        }
+
+        // Get all the chat sessions.
+        $allsessions = chat_get_sessions($messages, true);
+        // When showall is true, we should get 3 sessions.
+        $this->assertCount(3, $allsessions);
+
+        // Reverse sort sessions so they are in ascending order matching our expected session times and users.
+        $allsessions = array_reverse($allsessions);
+        foreach ($allsessions as $index => $session) {
+            // Check the session users.
+            $users = $sessionusers[$index];
+            $this->assertCount(count($users), $session->sessionusers);
+            // Check the message counts for each user in this session.
+            foreach ($users as $userid => $messagecount) {
+                $this->assertEquals($messagecount, $session->sessionusers[$userid]);
+            }
+
+            $sessionstart = $sessiontimes[$index]['start'];
+            $sessionend = $sessiontimes[$index]['end'];
+            $this->assertEquals($sessionstart, $session->sessionstart);
+            $this->assertEquals($sessionend, $session->sessionend);
+        }
+    }
+
     /**
      * Creates an action event.
      *