Add test for default freezing + noFreeze option

tests/browser/freeze.js

@@ -0,0 +1,46 @@
+const test = require('tape')
+const choo = require('../../')
+
+test('freeze (default)', function (t) {
+  t.plan(2)
+  const app = choo()
+
+  app.model({
+    state: {
+      foo: 'bar'
+    }
+  })
+
+  app.router((route) => [
+    route('/', function (state, prev, send) {
+      state.foo = ''
+      t.equal(state.foo, 'bar', 'cannot modify property')
+      state.bar = 'baz'
+      t.equal(state.bar, undefined, 'cannot add property')
+    })
+  ])
+
+  app.start()
+})
+
+test('noFreeze', function (t) {
+  t.plan(2)
+  const app = choo({noFreeze: true})
+
+  app.model({
+    state: {
+      foo: 'bar'
+    }
+  })
+
+  app.router((route) => [
+    route('/', function (state, prev, send) {
+      state.foo = ''
+      t.equal(state.foo, '', 'can modify property')
+      state.bar = 'baz'
+      t.equal(state.bar, 'baz', 'can add property')
+    })
+  ])
+
+  app.start()
+})