diff --git a/tests/phpunit/installation_test.php b/tests/phpunit/installation_test.php
index d0636ae..49ed6b0 100644
--- a/tests/phpunit/installation_test.php
+++ b/tests/phpunit/installation_test.php
@@ -71,7 +71,7 @@ class installation_test extends auth_outage_base_testcase {
         $progress = new progress_trace_buffer(new text_progress_trace(), false);
         core_plugin_manager::instance()->uninstall_plugin('auth_outage', $progress);
         $progress->finished();
-        self::assertContains('++ Success ++', $progress->get_buffer());
+        self::assertStringContainsString('++ Success ++', $progress->get_buffer());
 
         // Check ...
         self::assertSame(0, $DB->count_records_select('event', "eventtype = 'auth_outage'", null),
diff --git a/tests/phpunit/local/cli/cli_test.php b/tests/phpunit/local/cli/cli_test.php
index d589ccf..4cab5c6 100644
--- a/tests/phpunit/local/cli/cli_test.php
+++ b/tests/phpunit/local/cli/cli_test.php
@@ -81,8 +81,8 @@ class cli_test extends auth_outage_cli_testcase {
         $this->set_parameters(['-h']);
         $cli = new create();
         $output = $this->execute($cli);
-        self::assertContains('-h', $output);
-        self::assertContains('--help', $output);
+        self::assertStringContainsString('-h', $output);
+        self::assertStringContainsString('--help', $output);
     }
 
     /**
diff --git a/tests/phpunit/local/cli/create_test.php b/tests/phpunit/local/cli/create_test.php
index 4e8d707..e944bce 100644
--- a/tests/phpunit/local/cli/create_test.php
+++ b/tests/phpunit/local/cli/create_test.php
@@ -120,8 +120,8 @@ class create_test extends auth_outage_cli_testcase {
         $this->set_parameters(['--help']);
         $cli = new create();
         $output = $this->execute($cli);
-        self::assertContains('Creates', $output);
-        self::assertContains('--help', $output);
+        self::assertStringContainsString('Creates', $output);
+        self::assertStringContainsString('--help', $output);
     }
 
     /**
@@ -157,7 +157,7 @@ class create_test extends auth_outage_cli_testcase {
         $cli = new create();
         $cli->set_referencetime($now);
         $text = $this->execute($cli);
-        self::assertContains('created', $text);
+        self::assertStringContainsString('created', $text);
         // Check creted outage.
         list(, $id) = explode(':', $text);
         $id = (int)$id;
@@ -221,7 +221,7 @@ class create_test extends auth_outage_cli_testcase {
             'description' => 'Default Description',
         ]);
         $text = $this->execute($cli);
-        self::assertContains('created', $text);
+        self::assertStringContainsString('created', $text);
         // Check creted outage.
         list(, $id) = explode(':', $text);
         $id = (int)$id;
@@ -299,8 +299,8 @@ class create_test extends auth_outage_cli_testcase {
         $cli = new create();
         $cli->set_referencetime($now);
         $text = $this->execute($cli);
-        self::assertContains('created', $text);
-        self::assertContains('started', $text);
+        self::assertStringContainsString('created', $text);
+        self::assertStringContainsString('started', $text);
     }
 
     /**
diff --git a/tests/phpunit/local/cli/finish_test.php b/tests/phpunit/local/cli/finish_test.php
index ee97767..a2c290d 100644
--- a/tests/phpunit/local/cli/finish_test.php
+++ b/tests/phpunit/local/cli/finish_test.php
@@ -72,8 +72,8 @@ class finish_test extends auth_outage_cli_testcase {
         $this->set_parameters(['--help']);
         $cli = new finish();
         $text = $this->execute($cli);
-        self::assertContains('Finishes', $text);
-        self::assertContains('--help', $text);
+        self::assertStringContainsString('Finishes', $text);
+        self::assertStringContainsString('--help', $text);
     }
 
     /**
diff --git a/tests/phpunit/local/cli/waitforit_test.php b/tests/phpunit/local/cli/waitforit_test.php
index 419e8be..9b0d93c 100644
--- a/tests/phpunit/local/cli/waitforit_test.php
+++ b/tests/phpunit/local/cli/waitforit_test.php
@@ -78,8 +78,8 @@ class waitforit_test extends auth_outage_cli_testcase {
         $this->set_parameters(['--help']);
         $cli = new waitforit();
         $text = $this->execute($cli);
-        self::assertContains('Waits', $text);
-        self::assertContains('--help', $text);
+        self::assertStringContainsString('Waits', $text);
+        self::assertStringContainsString('--help', $text);
     }
 
     /**
@@ -151,9 +151,9 @@ class waitforit_test extends auth_outage_cli_testcase {
         $cli = new waitforit();
         $cli->set_referencetime($now);
         $output = $this->execute($cli);
-        self::assertContains('Verbose mode', $output);
-        self::assertContains('starting in 1 sec', $output);
-        self::assertContains('started', $output);
+        self::assertStringContainsString('Verbose mode', $output);
+        self::assertStringContainsString('starting in 1 sec', $output);
+        self::assertStringContainsString('started', $output);
     }
 
     /**
@@ -178,11 +178,11 @@ class waitforit_test extends auth_outage_cli_testcase {
             return $now;
         });
         $output = $this->execute($cli);
-        self::assertContains("starting in 45", $output);
-        self::assertContains("sleep 30 second", $output);
-        self::assertContains("starting in 15", $output);
-        self::assertContains("sleep 15 second", $output);
-        self::assertContains("started!", $output);
+        self::assertStringContainsString("starting in 45", $output);
+        self::assertStringContainsString("sleep 30 second", $output);
+        self::assertStringContainsString("starting in 15", $output);
+        self::assertStringContainsString("sleep 15 second", $output);
+        self::assertStringContainsString("started!", $output);
     }
 
     /**
diff --git a/tests/phpunit/local/controllers/infopage_test.php b/tests/phpunit/local/controllers/infopage_test.php
index bcaf9a4..881320f 100644
--- a/tests/phpunit/local/controllers/infopage_test.php
+++ b/tests/phpunit/local/controllers/infopage_test.php
@@ -103,7 +103,7 @@ class infopagecontroller_test extends auth_outage_base_testcase {
         ]);
         $info = new infopage(['outage' => $outage]);
         $output = $info->get_output();
-        self::assertContains('auth_outage_info', $output);
+        self::assertStringContainsString('auth_outage_info', $output);
     }
 
     /**
diff --git a/tests/phpunit/local/controllers/maintenance_static_page_test.php b/tests/phpunit/local/controllers/maintenance_static_page_test.php
index cd8f575..fffdfad 100644
--- a/tests/phpunit/local/controllers/maintenance_static_page_test.php
+++ b/tests/phpunit/local/controllers/maintenance_static_page_test.php
@@ -104,9 +104,9 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
                 '<body>Content<link rel="stylesheet" href="'.$externalcsslink.'"></body></html>';
         $generated = $this->generated_page_html($html);
 
-        self::assertContains('www.example.com/moodle/auth/outage/file.php?file=', $generated);
+        self::assertStringContainsString('www.example.com/moodle/auth/outage/file.php?file=', $generated);
         self::assertNotContains($localcsslink, $generated);
-        self::assertContains($externalcsslink, $generated);
+        self::assertStringContainsString($externalcsslink, $generated);
     }
 
     /**
@@ -174,9 +174,9 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
                 '<body><img src="'.$localimglink.'">Content<img src="'.$externalimglink.'" /></body></html>';
         $generated = $this->generated_page_html($html);
 
-        self::assertContains('www.example.com/moodle/auth/outage/file.php?file=', $generated);
+        self::assertStringContainsString('www.example.com/moodle/auth/outage/file.php?file=', $generated);
         self::assertNotContains($localimglink, $generated);
-        self::assertContains($externalimglink, $generated);
+        self::assertStringContainsString($externalimglink, $generated);
     }
 
      /**
@@ -190,7 +190,7 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         $generated = $this->generated_page_html($html);
 
         self::assertNotContains($link, $generated);
-        self::assertContains('www.example.com/moodle/auth/outage/file.php?file=', $generated);
+        self::assertStringContainsString('www.example.com/moodle/auth/outage/file.php?file=', $generated);
     }
 
      /**
@@ -207,7 +207,7 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         $generated = trim(file_get_contents($page->get_io()->get_template_file()));
 
         self::assertNotContains($link, $generated);
-        self::assertContains('www.example.com/moodle/auth/outage/file.php?file=preview%2F', $generated);
+        self::assertStringContainsString('www.example.com/moodle/auth/outage/file.php?file=preview%2F', $generated);
     }
 
     /**
@@ -303,7 +303,7 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
      */
     public function test_get_url_for_file() {
         $io = new maintenance_static_page_io();
-        self::assertContains('www.example.com/moodle/auth/outage/file.php?file=img.png', $io->get_url_for_file('img.png'));
+        self::assertStringContainsString('www.example.com/moodle/auth/outage/file.php?file=img.png', $io->get_url_for_file('img.png'));
     }
 
     /**
@@ -457,8 +457,8 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         set_config('remove_selectors', '#invalidid', 'auth_outage');
         $generated = $this->generated_page_html($html);
 
-        self::assertContains('removeme', $generated);
-        self::assertContains('Goodbye cruel world', $generated);
+        self::assertStringContainsString('removeme', $generated);
+        self::assertStringContainsString('Goodbye cruel world', $generated);
     }
 
     /**
@@ -472,7 +472,7 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         set_config('remove_selectors', '#invalidid', 'auth_outage');
         $generated = $this->generated_page_html($html);
 
-        self::assertContains('<meta http-equiv="refresh" content="300">', $generated);
+        self::assertStringContainsString('<meta http-equiv="refresh" content="300">', $generated);
     }
 
     /**
@@ -490,7 +490,7 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         $generated = trim(file_get_contents($page->get_io()->get_template_file()));
         return $generated;
 
-        self::assertContains('<meta http-equiv="refresh" content="5">', $generated);
+        self::assertStringContainsString('<meta http-equiv="refresh" content="5">', $generated);
     }
 
     /**
diff --git a/tests/phpunit/local/outagelib_test.php b/tests/phpunit/local/outagelib_test.php
index 4ff8567..729037b 100644
--- a/tests/phpunit/local/outagelib_test.php
+++ b/tests/phpunit/local/outagelib_test.php
@@ -99,8 +99,8 @@ class outagelib_test extends auth_outage_base_testcase {
         outagelib::reset_injectcalled();
         // Get full header to avoid interactions with other single inject plugins.
         $header1 = $OUTPUT->standard_top_of_body_html();
-        self::assertContains('<style>', $header1);
-        self::assertContains('<script>', $header1);
+        self::assertStringContainsString('<style>', $header1);
+        self::assertStringContainsString('<script>', $header1);
 
         // Should not inject more than once.
         $size = strlen($OUTPUT->standard_top_of_body_html());
@@ -142,8 +142,8 @@ class outagelib_test extends auth_outage_base_testcase {
 
         outagelib::reset_injectcalled();
         $header = outagelib::get_inject_code();
-        self::assertContains('<style>', $header);
-        self::assertContains('<script>', $header);
+        self::assertStringContainsString('<style>', $header);
+        self::assertStringContainsString('<script>', $header);
     }
 
     /**