utils: add use-case showing deepAssign does not replace, but merges

lib/common/spec/utils.spec.js

@@ -1,7 +1,7 @@
 import { RoutifyRuntime } from '../../runtime/Instance/RoutifyRuntime.js'
 
 import { RoutifyBuildtime } from '../../buildtime/RoutifyBuildtime.js'
-import { mockRoutes, next } from '../utils.js'
+import { deepAssign, mockRoutes, next } from '../utils.js'
 import { writable } from 'svelte/store'
 
 test('mock routes', () => {
@@ -66,6 +66,25 @@ test('next store value', () => {
     })
 })
 
+test('deepAssign replaces previous properties', () => {
+    const defaults = {
+        routifyDir: {
+            default: "src/routes"
+        }
+    };
+
+    const options = {
+        routifyDir: {
+            "bar": "src/routes/bar",
+            "foo": "src/routes/foo"
+        }
+    };
+
+    const assigned = deepAssign({}, defaults, options);
+
+    assert.equal(options, assigned);
+})
+
 // test('resolveValues', () => {
 //     const obj = {
 //         plan: { text: 'nothing to see here' },