[fix] add test folder to includes

Also add some notes to tsconfig/jsonfig
Fixes #5833

Author: dummdidumm

.changeset/hot-lions-cough.md

@@ -0,0 +1,5 @@
+---
+'create-svelte': patch
+---
+
+Add notes about includes/excludes and path aliases

.changeset/warm-pots-melt.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Add test folder to generated tsconfig

packages/create-svelte/shared/+checkjs/jsconfig.json

@@ -10,4 +10,8 @@
 		"sourceMap": true,
 		"strict": true
 	}
+	// Path aliases are handled by https://kit.svelte.dev/docs/configuration#alias and https://kit.svelte.dev/docs/configuration#files
+	//
+	// If you want to overwrite includes/excludes, make sure to copy over the relevant includes/excludes
+	// from the referenced tsconfig.json - TypeScript does not merge them in
 }

packages/create-svelte/shared/+typescript/tsconfig.json

@@ -10,4 +10,8 @@
 		"sourceMap": true,
 		"strict": true
 	}
+	// Path aliases are handled by https://kit.svelte.dev/docs/configuration#alias and https://kit.svelte.dev/docs/configuration#files
+	//
+	// If you want to overwrite includes/excludes, make sure to copy over the relevant includes/excludes
+	// from the referenced tsconfig.json - TypeScript does not merge them in
 }

packages/kit/src/core/sync/write_tsconfig.js

@@ -53,6 +53,12 @@ export function write_tsconfig(config, cwd = process.cwd()) {
 		include.push(config_relative(`${relative}/**/*.ts`));
 		include.push(config_relative(`${relative}/**/*.svelte`));
 	}
+	// Test folder is a special case - we advocate putting tests in a top-level test folder
+	// and it's not configurable (should we make it?)
+	const test_folder = project_relative('test');
+	include.push(config_relative(`${test_folder}/**/*.js`));
+	include.push(config_relative(`${test_folder}/**/*.ts`));
+	include.push(config_relative(`${test_folder}/**/*.svelte`));
 
 	write_if_changed(
 		out,