Closes #4297

ChangeLog-9.3.md

@@ -156,6 +156,7 @@ Here is a detailed list of changes for the configuration of code coverage and lo
 
 ### Removed
 
+* [#4297](https://github.com/sebastianbergmann/phpunit/issues/4297): Deprecate `at()` matcher
 * The `cacheTokens` attribute is no longer supported in XML configuration files
 
 [9.3.0]: https://github.com/sebastianbergmann/phpunit/compare/9.2...master

src/Framework/MockObject/Rule/InvokedAtIndex.php

@@ -15,6 +15,9 @@
 
 /**
  * @internal This class is not covered by the backward compatibility promise for PHPUnit
+ *
+ * @deprecated https://github.com/sebastianbergmann/phpunit/issues/4297
+ * @codeCoverageIgnore
  */
 final class InvokedAtIndex extends InvocationOrder
 {

src/Framework/TestCase.php

@@ -22,6 +22,7 @@
 use function array_flip;
 use function array_keys;
 use function array_merge;
+use function array_pop;
 use function array_search;
 use function array_unique;
 use function array_values;
@@ -32,6 +33,7 @@
 use function class_exists;
 use function clearstatcache;
 use function count;
+use function debug_backtrace;
 use function defined;
 use function explode;
 use function get_class;
@@ -410,9 +412,26 @@ public static function atMost(int $allowedInvocations): InvokedAtMostCountMatche
     /**
      * Returns a matcher that matches when the method is executed
      * at the given index.
+     *
+     * @deprecated https://github.com/sebastianbergmann/phpunit/issues/4297
+     * @codeCoverageIgnore
      */
     public static function at(int $index): InvokedAtIndexMatcher
     {
+        $stack = debug_backtrace();
+
+        while (!empty($stack)) {
+            $frame = array_pop($stack);
+
+            if (isset($frame['object']) && $frame['object'] instanceof self) {
+                $frame['object']->addWarning(
+                    'The at() matcher has been deprecated. It will be removed in PHPUnit 10. Please refactor your test to not rely on the order in which methods are invoked.'
+                );
+
+                break;
+            }
+        }
+
         return new InvokedAtIndexMatcher($index);
     }