diff -u b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
--- b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
+++ b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
@@ -220,6 +220,7 @@
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
    *   Use $this->assertSession()->fieldExists() or
+   *   $this->assertSession()->buttonExists() or
    *   $this->assertSession()->fieldValueEquals() instead.
    */
   protected function assertFieldByName($name, $value = NULL) {
@@ -239,6 +240,7 @@
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
    *   Use $this->assertSession()->fieldNotExists() or
+   *   $this->assertSession()->buttonNotExists() or
    *   $this->assertSession()->fieldValueNotEquals() instead.
    */
   protected function assertNoFieldByName($name, $value = '') {
@@ -246,7 +248,7 @@
   }
 
   /**
-   * Asserts that a field exists with the given ID and value.
+   * Asserts that a field exists with the given ID and val.ue.
    *
    * @param string $id
    *   ID of field to assert.
@@ -260,6 +262,7 @@
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
    *   Use $this->assertSession()->fieldExists() or
+   *   $this->assertSession()->buttonExists() or
    *   $this->assertSession()->fieldValueEquals() instead.
    */
   protected function assertFieldById($id, $value = '') {
@@ -273,7 +276,8 @@
    *   Name or ID of field to assert.
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
-   *   Use $this->assertSession()->fieldExists() instead.
+   *   Use $this->assertSession()->fieldExists() or
+   *   $this->assertSession()->buttonExists() instead.
    */
   protected function assertField($field) {
     $this->assertFieldByXPath($this->constructFieldXpath('name', $field) . '|' . $this->constructFieldXpath('id', $field));
@@ -286,7 +290,8 @@
    *   Name or ID of field to assert.
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
-   *   Use $this->assertSession()->fieldNotExists() instead.
+   *   Use $this->assertSession()->fieldNotExists() or
+   *   $this->assertSession()->buttonNotExists() instead.
    */
   protected function assertNoField($field) {
     $this->assertNoFieldByXPath($this->constructFieldXpath('name', $field) . '|' . $this->constructFieldXpath('id', $field), NULL);
@@ -410,6 +415,7 @@
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
    *   Use $this->assertSession()->fieldNotExists() or
+   *   $this->assertSession()->buttonNotExists() or
    *   $this->assertSession()->fieldValueNotEquals() instead.
    */
   protected function assertNoFieldById($id, $value = '') {
@@ -574,16 +580,11 @@
         }
 
         if ($found) {
-          throw new ExpectationException(new FormattableMarkup('The field resulting from :xpath was found with the provided value :value.', [
-            ':xpath' => $xpath,
-            ':value' => $value,
-          ]), $this->getSession()->getDriver());
+          throw new ExpectationException(sprintf('The field resulting from %s was found with the provided value %s.', $xpath, $value), $this->getSession()->getDriver());
         }
       }
       else {
-        throw new ExpectationException(new FormattableMarkup('The field resulting from :xpath was found.', [
-          ':xpath' => $xpath,
-        ]), $this->getSession()->getDriver());
+        throw new ExpectationException(sprintf('The field resulting from %s was found.', $xpath), $this->getSession()->getDriver());
       }
     }
   }
@@ -613,7 +614,7 @@
         foreach ($fields as $field) {
           if ($field->getAttribute('type') == 'checkbox') {
             // Checkbox with the correct checked state.
-            $found = $field->isChecked() == $value;
+            $found = $field->isChecked() === $value;
           }
           elseif ($field->getTagName() == 'select' && $field->find('xpath', '//option[@value = ' . (new Escaper())->escapeLiteral($value) . ' and @selected = "selected"]')) {
             // Select element with an option.