diff --git a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
index 81da04a..5785a7d 100644
--- a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
+++ b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
@@ -94,6 +94,58 @@ protected function assertNoText($text) {
   }
 
   /**
+   * Passes if the text is found ONLY ONCE on the text version of the page.
+   *
+   * The text version is the equivalent of what a user would see when viewing
+   * through a web browser. In other words the HTML has been filtered out of
+   * the contents.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages with t(). If left blank, a default message will be displayed.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->getSession()->getPage()->getText() and substr_count() instead.
+   */
+  protected function assertUniqueText($text, $message = NULL) {
+    // Cast MarkupInterface objects to string.
+    $text = (string) $text;
+
+    $message = $message ?: "'$text' found only once on the page";
+    $page_text = $this->getSession()->getPage()->getText();
+    $nr_found = substr_count($page_text, $text);
+    $this->assertSame(1, $nr_found, $message);
+  }
+
+  /**
+   * Passes if the text is found MORE THAN ONCE on the text version of the page.
+   *
+   * The text version is the equivalent of what a user would see when viewing
+   * through a web browser. In other words the HTML has been filtered out of
+   * the contents.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages with t(). If left blank, a default message will be displayed.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->getSession()->getPage()->getText() and substr_count() instead.
+   */
+  protected function assertNoUniqueText($text, $message = '') {
+    // Cast MarkupInterface objects to string.
+    $text = (string) $text;
+
+    $message = $message ?: "'$text' found more than once on the page";
+    $page_text = $this->getSession()->getPage()->getText();
+    $nr_found = substr_count($page_text, $text);
+    $this->assertGreaterThan(1, $nr_found, $message);
+  }
+
+  /**
    * Asserts the page responds with the specified response code.
    *
    * @param int $code
@@ -371,12 +423,18 @@ protected function assertNoOption($id, $option) {
    *   ID of select field to assert.
    * @param string $option
    *   Option to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages with t(). If left blank, a default message will be displayed.
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
-   *   Use $this->assertSession()->optionSelected() instead.
+   *   Use $this->assertSession()->optionExists() instead and check the
+   *   "selected" attribute yourself.
    */
-  protected function assertOptionSelected($id, $option) {
-    $this->assertSession()->optionSelected($id, $option);
+  protected function assertOptionSelected($id, $option, $message = NULL) {
+    $option_field = $this->assertSession()->optionExists($id, $option);
+    $message = $message ?: "Option $option for field $id is selected.";
+    $this->assertTrue($option_field->hasAttribute('selected'), $message);
   }
 
   /**
@@ -436,6 +494,19 @@ protected function assertNoEscaped($raw) {
   }
 
   /**
+   * Triggers a pass if the Perl regex pattern is found in the raw content.
+   *
+   * @param string $pattern
+   *   Perl regex to look for including the regex delimiters.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->responseMatches() instead.
+   */
+  protected function assertPattern($pattern) {
+    $this->assertSession()->responseMatches($pattern);
+  }
+
+  /**
    * Asserts whether an expected cache tag was present in the last response.
    *
    * @param string $expected_cache_tag
diff --git a/core/tests/Drupal/Tests/WebAssert.php b/core/tests/Drupal/Tests/WebAssert.php
index d4cffd8..6156dda 100644
--- a/core/tests/Drupal/Tests/WebAssert.php
+++ b/core/tests/Drupal/Tests/WebAssert.php
@@ -191,29 +191,6 @@ public function optionNotExists($select, $option, TraversableElement $container
   }
 
   /**
-   * Checks that a specific option in a select field is selected.
-   *
-   * @param string $select
-   *   One of id|name|label|value for the select field.
-   * @param string $option
-   *   The option value.
-   * @param \Behat\Mink\Element\TraversableElement $container
-   *   (optional) The document to check against. Defaults to the current page.
-   *
-   * @return \Behat\Mink\Element\NodeElement
-   *   The matching option element
-   *
-   * @throws \Behat\Mink\Exception\ElementNotFoundException
-   *   When the element doesn't exist.
-   */
-  public function optionSelected($select, $option, TraversableElement $container = NULL) {
-    $option_field = $this->optionExists($select, $option, $container);
-    $this->assert(!empty($option_field->getAttribute('selected')), sprintf('Option "%s" in select "%s" is not selected as expected.', $option, $select));
-
-    return $option_field;
-  }
-
-  /**
    * Pass if the page title is the given string.
    *
    * @param string $expected_title