Change default status to 404 without affecting Koa default semantics

#57

src/__tests__/index.node.js

@@ -0,0 +1,58 @@
+/** Copyright (c) 2018 Uber Technologies, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import test from 'tape-cup';
+import App from 'fusion-core';
+
+import {getSimulator} from '../index.js';
+
+test('status is 404 if ctx.body is never updated', async t => {
+  const app = new App('el', el => el);
+  const ctx = await getSimulator(app).request('/');
+  t.equals(ctx.status, 404, 'status defaults to 404');
+  t.end();
+});
+
+test('status is 200 if ctx.body is updated in request', async t => {
+  const app = new App('el', el => el);
+  app.middleware((ctx, next) => {
+    ctx.body = {ok: 1};
+    return next();
+  });
+  const ctx = await getSimulator(app).request('/');
+  t.equals(ctx.status, 200, 'status defaults to 200');
+  t.end();
+});
+
+test('status is set if ctx.status is updated in request', async t => {
+  const app = new App('el', () => 'hello');
+  app.middleware((ctx, next) => {
+    ctx.status = 500;
+    ctx.body = {error: 'error'};
+    return next();
+  });
+  const ctx = await getSimulator(app).render('/');
+  t.equals(ctx.status, 500, 'status is set');
+  t.end();
+});
+
+test('status is 200 if ctx.body is updated in render', async t => {
+  const app = new App('el', () => 'hello');
+  const ctx = await getSimulator(app).render('/');
+  t.equals(ctx.status, 200, 'status defaults to 200');
+  t.end();
+});
+
+test('status is set if ctx.status is updated in render', async t => {
+  const app = new App('el', () => 'hello');
+  app.middleware((ctx, next) => {
+    ctx.status = 500;
+    return next();
+  });
+  const ctx = await getSimulator(app).render('/');
+  t.equals(ctx.status, 500, 'status is set');
+  t.end();
+});

src/mock-context.js

@@ -36,17 +36,16 @@ export function mockContext(url: string, options: *): Context {
   //$FlowFixMe
   req = Object.assign({headers: {}, socket}, Stream.Readable.prototype, req);
   //$FlowFixMe
-  res = Object.assign({_headers: {}, socket}, Stream.Writable.prototype, res);
+  res = Object.assign({_headers: {}, socket}, Stream.Writable.prototype, res, {
+    statusCode: 404,
+  });
   req.socket.remoteAddress = req.socket.remoteAddress || '127.0.0.1';
   res.getHeader = k => res._headers[k.toLowerCase()];
   res.setHeader = (k, v) => (res._headers[k.toLowerCase()] = v);
   res.removeHeader = k => delete res._headers[k.toLowerCase()];
 
-  const app = new Koa();
   //$FlowFixMe
-  const ctx = app.createContext(req, res);
-  ctx.status = 404;
-  return ctx;
+  return new Koa().createContext(req, res);
 }
 
 export function renderContext(url: string, options: any): Context {