{"id":480,"date":"2010-02-01T18:07:18","date_gmt":"2010-02-01T16:07:18","guid":{"rendered":"http:\/\/www.limilabs.com\/blog\/?p=480"},"modified":"2010-02-01T18:07:18","modified_gmt":"2010-02-01T16:07:18","slug":"testing-datetime-now","status":"publish","type":"post","link":"https:\/\/www.limilabs.com\/blog\/testing-datetime-now","title":{"rendered":"Testing DateTime.Now"},"content":{"rendered":"

\"\"<\/p>\n

When you are doing Test Driven Development (TDD) many time during the testing phase you’ll find yourself with a code that depends on current time.<\/p>\n

It’s not possible write tests for this code as DateTime.Now changes constantly<\/strong>.<\/p>\n

Let’s take a look at following method:<\/p>\n

\npublic string CreateName(...)\n{\n   return "name " + DateTime.Now;\n}\n<\/pre>\n
The solution to this problem is simple. We’ll introduce Clock<\/em> class with the same interface as DateTime<\/em>:<\/p>\n
\npublic string CreateName(...)\n{\n   return "name " + Clock.Now;\n}\n<\/pre>\n
We’d like the test to look something like this:<\/p>\n
\n[Test]\npublic void CreateName_AddsCurrentTimeAtEnd()\n{\n    using (Clock.NowIs(new DateTime(2010, 12, 31, 23, 59, 00)))\n    {\n        string name = new ReportNameService().CreateName(...);\n        Assert.AreEqual("name 2010-12-31 23:59:00", name);\n    }\n}\n<\/pre>\n
Tests should not leave any side effects<\/strong>. This is why we are using IDisposable pattern. After text execution Clock.Now<\/em> is reverted and again returns current time.<\/p>\n
Finally this is how Clock<\/em> class looks like:<\/p>\n
\npublic class Clock : IDisposable\n{\n    private static DateTime? _nowForTest;\n\n    public static DateTime Now\n    {\n        get { return _nowForTest ?? DateTime.Now; }\n    }\n\n    public static IDisposable NowIs(DateTime dateTime)\n    {\n        _nowForTest = dateTime;\n        return new Clock();\n    }\n\n    public void Dispose()\n    {\n        _nowForTest = null;\n    }\n};\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
When you are doing Test Driven Development (TDD) many time during the testing phase you’ll find yourself with a code that depends on current time. It’s not possible write tests for this code as DateTime.Now changes constantly. Let’s take a look at following method: public string CreateName(…) { return "name " + DateTime.Now; } The […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[15,56],"class_list":["post-480","post","type-post","status-publish","format-standard","hentry","category-programming","tag-c","tag-unit-testing"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/posts\/480"}],"collection":[{"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/comments?post=480"}],"version-history":[{"count":0,"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/posts\/480\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/media?parent=480"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/categories?post=480"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.limilabs.com\/blog\/wp-json\/wp\/v2\/tags?post=480"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}