Ignore param matchers that match .{spec,test}.{js,ts}

.changeset/healthy-lizards-drum.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Ignore `*.test.js` and `*.spec.js` files in `params` directory

documentation/docs/30-advanced/10-advanced-routing.md

@@ -90,6 +90,8 @@ export function match(param) {
 
 If the pathname doesn't match, SvelteKit will try to match other routes (using the sort order specified below), before eventually returning a 404.
 
+Each module in the `params` directory corresponds to a matcher, with the exception of `*.test.js` and `*.spec.js` files which may be used to unit test your matchers.
+
 > Matchers run both on the server and in the browser.
 
 ## Sorting

packages/kit/src/core/sync/create_manifest_data/index.js

@@ -76,6 +76,9 @@ function create_matchers(config, cwd) {
 					matchers[type] = matcher_file;
 				}
 			} else {
+				// Allow for matcher test collocation
+				if (type.endsWith('.test') || type.endsWith('.spec')) continue;
+
 				throw new Error(
 					`Matcher names can only have underscores and alphanumeric characters — "${file}" is invalid`
 				);