diff --git a/src/lib/directives/transition.directives.ts b/src/lib/directives/transition.directives.ts
index 9a2d8e82..51718ce6 100644
--- a/src/lib/directives/transition.directives.ts
+++ b/src/lib/directives/transition.directives.ts
@@ -2,9 +2,11 @@ import {
   fade as svelteFade,
   fly as svelteFly,
   scale as svelteScale,
+  slide as svelteSlide,
   type FadeParams,
   type FlyParams,
   type ScaleParams,
+  type SlideParams,
   type TransitionConfig,
 } from "svelte/transition";
 
@@ -67,3 +69,23 @@ export const testSafeScale = (
 
   return svelteScale(node, params);
 };
+
+/**
+ * A wrapper around Svelte's `slide` transition that disables itself in test mode.
+ *
+ * Prevents the test error "Cannot set properties of undefined (setting 'onfinish')".
+ *
+ * @param {HTMLElement} node - The HTML element to apply the transition to.
+ * @param {SlideParams} [params] - Optional parameters for the slide transition.
+ * @returns {TransitionConfig} The transition configuration, or an empty object in test mode.
+ */
+export const testSafeSlide = (
+  node: HTMLElement,
+  params?: SlideParams | undefined,
+): TransitionConfig => {
+  if (process.env.NODE_ENV === "test") {
+    return {};
+  }
+
+  return svelteSlide(node, params);
+};