From d04be35e204ed269337c1966270f67012f9d8ccc Mon Sep 17 00:00:00 2001
From: Bhavya Dhiman <bhavyadhiman7@gmail.com>
Date: Mon, 16 Mar 2026 05:01:39 +0530
Subject: [PATCH] achieve 100% test coverage in expressjs

---
 test/app.listen.js          |  14 +++
 test/req.is.js              |  16 ++++
 test/res.append.js          |  16 ++++
 test/res.jsonp.js           |  22 +++++
 test/res.redirect.js        |  42 +++++++++
 test/res.sendFile.guards.js | 168 ++++++++++++++++++++++++++++++++++++
 test/view.js                | 125 +++++++++++++++++++++++++++
 7 files changed, 403 insertions(+)
 create mode 100644 test/res.sendFile.guards.js
 create mode 100644 test/view.js

diff --git a/test/app.listen.js b/test/app.listen.js
index 3ef94ff184a..3d1bd3d27e5 100644
--- a/test/app.listen.js
+++ b/test/app.listen.js
@@ -41,6 +41,20 @@ describe('app.listen()', function(){
     const server = app.listen();
     server.close(done);
   });
+
+  it('should not invoke callback more than once', function (done) {
+    var app = express()
+    var count = 0
+    var server = app.listen(0, function () {
+      count++
+      server.emit('error', new Error('boom'))
+      setImmediate(function () {
+        assert.strictEqual(count, 1)
+        server.close(done)
+      })
+    })
+  })
+
   it('server.address() gives a { address, port, family } object', function (done) {
     const app = express();
     const server = app.listen(0, () => {
diff --git a/test/req.is.js b/test/req.is.js
index c5904dd600a..d1e44e0aca0 100644
--- a/test/req.is.js
+++ b/test/req.is.js
@@ -166,4 +166,20 @@ describe('req.is()', function () {
       .expect(200, '"application/json"', done)
     })
   })
+
+  describe('when given an array of types', function () {
+    it('should not flatten the argument', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.json(req.is(['text/*', 'application/json']))
+      })
+
+      request(app)
+      .post('/')
+      .type('application/json')
+      .send('{}')
+      .expect(200, '"application/json"', done)
+    })
+  })
 })
diff --git a/test/res.append.js b/test/res.append.js
index 2dd17a3a1fb..3058ce92ee4 100644
--- a/test/res.append.js
+++ b/test/res.append.js
@@ -82,6 +82,22 @@ describe('res', function () {
         .end(done)
     })
 
+    it('should append an array to an existing single value', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.set('Set-Cookie', 'foo=bar')
+        res.append('Set-Cookie', ['fizz=buzz', 'pet=tobi'])
+        res.end()
+      })
+
+      request(app)
+        .get('/')
+        .expect(200)
+        .expect(shouldHaveHeaderValues('Set-Cookie', ['foo=bar', 'fizz=buzz', 'pet=tobi']))
+        .end(done)
+    })
+
     it('should work together with res.cookie', function (done) {
       var app = express()
 
diff --git a/test/res.jsonp.js b/test/res.jsonp.js
index e043a3b07f2..9b1d9777847 100644
--- a/test/res.jsonp.js
+++ b/test/res.jsonp.js
@@ -215,6 +215,28 @@ describe('res', function(){
           .expect('Content-Type', 'text/javascript; charset=utf-8')
           .expect(200, /cb\(42\)/, done)
       })
+
+      it('should handle non-string stringify return values', function (done) {
+        var app = express()
+
+        app.use(function (req, res) {
+          var original = JSON.stringify
+          JSON.stringify = function () {
+            return 42
+          }
+
+          try {
+            res.jsonp('ignored')
+          } finally {
+            JSON.stringify = original
+          }
+        })
+
+        request(app)
+          .get('/?callback=cb')
+          .expect('Content-Type', 'text/javascript; charset=utf-8')
+          .expect(200, /cb\(42\)/, done)
+      })
     })
 
     describe('when given an array', function () {
diff --git a/test/res.redirect.js b/test/res.redirect.js
index 8d2b164e4a2..25060cca191 100644
--- a/test/res.redirect.js
+++ b/test/res.redirect.js
@@ -211,4 +211,46 @@ describe('res', function(){
         .end(done)
     })
   })
+
+  describe('when given invalid arguments', function () {
+    it('should handle missing url argument', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.redirect('')
+      })
+
+      request(app)
+        .get('/')
+        .expect(302)
+        .expect('Location', '')
+        .end(done)
+    })
+
+    it('should coerce when url is not a string', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.redirect(42)
+      })
+
+      request(app)
+        .get('/')
+        .expect(302)
+        .expect('Location', '42')
+        .end(done)
+    })
+
+    it('should fail when status is not a number', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.redirect('302', '/somewhere')
+      })
+
+      request(app)
+        .get('/')
+        .expect(500, done)
+    })
+  })
 })
diff --git a/test/res.sendFile.guards.js b/test/res.sendFile.guards.js
new file mode 100644
index 00000000000..1b00201ec58
--- /dev/null
+++ b/test/res.sendFile.guards.js
@@ -0,0 +1,168 @@
+'use strict'
+
+var assert = require('node:assert')
+var EventEmitter = require('node:events').EventEmitter
+var Module = require('node:module')
+
+var responseModulePath = require.resolve('../lib/response')
+
+function loadMockedResponse(sendMock, onFinishedMock) {
+  var originalLoad = Module._load
+  var savedCache = require.cache[responseModulePath]
+
+  delete require.cache[responseModulePath]
+
+  Module._load = function (request, parent, isMain) {
+    if (request === 'send') return sendMock
+    if (request === 'on-finished') return onFinishedMock
+    return originalLoad.apply(this, arguments)
+  }
+
+  var mocked = require('../lib/response')
+
+  Module._load = originalLoad
+
+  if (savedCache) {
+    require.cache[responseModulePath] = savedCache
+  } else {
+    delete require.cache[responseModulePath]
+  }
+
+  return mocked
+}
+
+function createMockRes(response) {
+  var res = Object.create(response)
+  res.req = {
+    next: function () {}
+  }
+  res.app = {
+    enabled: function () {
+      return true
+    }
+  }
+  res.setHeader = function () {}
+  return res
+}
+
+function runScenario(setup, done) {
+  var callbackCount = 0
+  var callbackErr
+  var file
+
+  function sendMock() {
+    file = new EventEmitter()
+    file.pipe = function (res) {
+      setup.pipe(file, res)
+    }
+    return file
+  }
+
+  function onFinishedMock(res, onfinish) {
+    setup.onFinished(file, onfinish)
+  }
+
+  var response = loadMockedResponse(sendMock, onFinishedMock)
+  var res = createMockRes(response)
+
+  response.sendFile.call(res, '/tmp/fake.txt', function (err) {
+    callbackCount++
+    callbackErr = err || null
+    setup.onCallback && setup.onCallback(err)
+  })
+
+  setImmediate(function () {
+    setup.assert(callbackCount, callbackErr)
+    done()
+  })
+}
+
+describe('res.sendFile() internal guards', function () {
+  it('should ignore ECONNRESET finish after already ended (onaborted done-guard)', function (done) {
+    runScenario({
+      pipe: function (file) {
+        file.emit('end')
+      },
+      onFinished: function (file, onfinish) {
+        setImmediate(function () {
+          onfinish({ code: 'ECONNRESET' })
+        })
+      },
+      assert: function (count, err) {
+        assert.strictEqual(count, 1)
+        assert.strictEqual(err, null)
+      }
+    }, done)
+  })
+
+  it('should ignore directory event after error (ondirectory done-guard)', function (done) {
+    runScenario({
+      pipe: function (file) {
+        file.emit('error', new Error('boom'))
+        file.emit('directory')
+      },
+      onFinished: function () {},
+      assert: function (count, err) {
+        assert.strictEqual(count, 1)
+        assert.ok(err)
+      }
+    }, done)
+  })
+
+  it('should ignore error event after end (onerror done-guard)', function (done) {
+    runScenario({
+      pipe: function (file) {
+        file.emit('end')
+        file.emit('error', new Error('late error'))
+      },
+      onFinished: function () {},
+      assert: function (count, err) {
+        assert.strictEqual(count, 1)
+        assert.strictEqual(err, null)
+      }
+    }, done)
+  })
+
+  it('should ignore end event after error (onend done-guard)', function (done) {
+    runScenario({
+      pipe: function (file) {
+        file.emit('error', new Error('boom'))
+        file.emit('end')
+      },
+      onFinished: function () {},
+      assert: function (count, err) {
+        assert.strictEqual(count, 1)
+        assert.ok(err)
+      }
+    }, done)
+  })
+
+  it('should handle non-ECONNRESET finish errors via onerror', function (done) {
+    runScenario({
+      pipe: function () {},
+      onFinished: function (file, onfinish) {
+        onfinish({ code: 'EPIPE' })
+      },
+      assert: function (count, err) {
+        assert.strictEqual(count, 1)
+        assert.ok(err)
+        assert.strictEqual(err.code, 'EPIPE')
+      }
+    }, done)
+  })
+
+  it('should skip finish completion when done before setImmediate', function (done) {
+    runScenario({
+      pipe: function (file) {
+        file.emit('end')
+      },
+      onFinished: function (file, onfinish) {
+        onfinish()
+      },
+      assert: function (count, err) {
+        assert.strictEqual(count, 1)
+        assert.strictEqual(err, null)
+      }
+    }, done)
+  })
+})
diff --git a/test/view.js b/test/view.js
new file mode 100644
index 00000000000..5cead278746
--- /dev/null
+++ b/test/view.js
@@ -0,0 +1,125 @@
+'use strict'
+
+var assert = require('node:assert')
+var express = require('..')
+var path = require('node:path')
+var request = require('supertest')
+var tmpl = require('./support/tmpl')
+
+describe('View', function () {
+  it('should handle missing options object', function () {
+    assert.throws(function () {
+      new View('name')
+    }, /No default engine was specified and no extension was provided\./)
+  })
+
+  describe('integration', function () {
+    it('should throw error via app.render() without view engine or extension', function (done) {
+      var app = express()
+
+      try {
+        app.render('user', function (err) {
+          done(new Error('Should have thrown'))
+        })
+        done(new Error('Should have thrown'))
+      } catch (err) {
+        assert.match(err.message, /No default engine was specified and no extension was provided\./)
+        done()
+      }
+    })
+
+    it('should throw error via res.render() without view engine or extension', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.render('user')
+      })
+
+      request(app)
+        .get('/')
+        .expect(500, /No default engine was specified and no extension was provided\./, done)
+    })
+
+    it('should throw error for non-existent view engine', function (done) {
+      var app = express()
+
+      app.set('view engine', 'unknown')
+      app.set('views', path.join(__dirname, 'fixtures'))
+
+      try {
+        app.render('user', function (err) {
+          done(new Error('Should have thrown'))
+        })
+        done(new Error('Should have thrown'))
+      } catch (err) {
+        assert.match(err.message, /Cannot find module/)
+        done()
+      }
+    })
+
+    it('should throw error via res.render() for non-existent view engine', function (done) {
+      var app = express()
+
+      app.set('view engine', 'unknown')
+      app.set('views', path.join(__dirname, 'fixtures'))
+
+      app.use(function (req, res) {
+        res.render('user')
+      })
+
+      request(app)
+        .get('/')
+        .expect(500, /Cannot find module/, done)
+    })
+
+    it('should successfully render via res.render() with valid engine', function (done) {
+      var app = express()
+
+      app.engine('tmpl', tmpl)
+      app.set('view engine', 'tmpl')
+      app.set('views', path.join(__dirname, 'fixtures'))
+      app.locals.user = { name: 'tobi' }
+
+      app.use(function (req, res) {
+        res.render('user')
+      })
+
+      request(app)
+        .get('/')
+        .expect('<p>tobi</p>', done)
+    })
+
+    it('should reuse cached engine on second render', function (done) {
+      var app = express()
+
+      app.engine('tmpl', tmpl)
+      app.set('view engine', 'tmpl')
+      app.set('views', path.join(__dirname, 'fixtures'))
+      app.locals.user = { name: 'loki' }
+
+      var renderCount = 0
+      app.use(function (req, res) {
+        if (renderCount === 0) {
+          renderCount++
+          res.render('user', function (err, html) {
+            if (err) return res.send(500)
+            // render again to test cached engine
+            res.render('user', function (err, html2) {
+              if (err) return res.send(500)
+              res.send(html2)
+            })
+          })
+        }
+      })
+
+      request(app)
+        .get('/')
+        .expect('<p>loki</p>', done)
+    })
+  })
+})
+
+function View(name) {
+  var View = require('../lib/view')
+  return new View(name)
+}