diff --git a/core/themes/classy/templates/simpletest-result-summary.html.twig b/core/themes/classy/templates/simpletest-result-summary.html.twig
new file mode 100644
index 0000000..2f87ed0
--- /dev/null
+++ b/core/themes/classy/templates/simpletest-result-summary.html.twig
@@ -0,0 +1,22 @@
+{#
+/**
+ * @file
+ * Default theme implementation for simpletest result summaries.
+ *
+ * Available variables:
+ * - label: An optional label to be rendered before the results.
+ * - items: Pluralized summaries for each result type (number of passes, fails,
+ *   exceptions, and debug messages).
+ * - pass: The number of passes.
+ * - fail: The number of fails.
+ * - exception: The number of exceptions.
+ * - debug: The number of debug messages.
+ *
+ * @see template_preprocess_simpletest_result_summary()
+ *
+ * @ingroup themeable
+ */
+#}
+<div class="simpletest-{{ fail + exception == 0 ? 'pass' : 'fail' }}">
+  {{ label }} {{ items|join(', ') }}
+</div>