Shouldly断言库如何知道断言所应用于的表达式? [英] How does the Shouldly assertion library know the expression the assertion was applied to?

问题描述

针对.NET的断言库应该以某种方式知道调用断言方法的表达式，因此它能够将其显示在消息中.我试图找出它是如何工作的，但在源代码中迷路了.我怀疑它会查看已编译的代码，但我真的很想看看这是如何发生的.从文档中

The Shouldly assertion library for .NET somehow knows what expression the assertion method was called on so it is able to display it into the message. I tried to find out how it works but got lost in the source code. I suspect it looks into the compiled code but I would really like to see how this happens. From the documentation

map.IndexOfValue("boo").ShouldBe(2); // -> map.IndexOfValue("boo") should be 2 but was 1

以某种方式应该知道表达式map.IndexOfValue("boo")并能够在测试失败消息中显示它.有谁知道这是怎么发生的?

Somehow Shouldly knows the expression map.IndexOfValue("boo") and was able to display it in the test failure message. Does anyone know how this happens?

推荐答案

看看代码，这很聪明.

魔术发生在 ActualCodeTextGetter 类中.首先，它使用StackTrace检索源代码文件的行:

The magic is happening in the ActualCodeTextGetter class. First, it retrieves the line of the source code file by using the StackTrace:

  StackTrace stackTrace = trace ?? new StackTrace(true);

  // Cut for brevity

  StackFrame stackFrame = frame;
  this.ShouldlyFrameIndex = index - 1;
  string fileName = stackFrame.GetFileName();
  this._determinedOriginatingFrame = fileName != null && File.Exists(fileName);
  this._shouldMethod = this.ShouldlyFrame.GetMethod().Name;
  this.FileName = fileName;
  this.LineNumber = stackFrame.GetFileLineNumber() - 1;

一旦有了源代码文件的名称，以及语句的行和偏移量，就可以直接读取文件:

Once it has the name of the source code file, along with the line and offset of the statement, it's just a matter of reading directly the file:

private string GetCodePart()
{
  string str = "Shouldly uses your source code to generate its great error messages, build your test project with full debug information to get better error messages\nThe provided expression";
  if (this._determinedOriginatingFrame)
  {
    string codeLines = string.Join("\n", ((IEnumerable<string>) File.ReadAllLines(this.FileName)).Skip<string>(this.LineNumber).ToArray<string>());
    int indexOfMethod = codeLines.IndexOf(this._shouldMethod);
    if (indexOfMethod > 0)
      str = codeLines.Substring(0, indexOfMethod - 1).Trim();
    str = !str.EndsWith("Should") ? str.RemoveVariableAssignment().RemoveBlock() : this.GetCodePartFromParameter(indexOfMethod, codeLines, str);
  }
  return str;
}

还有很多逻辑可以精确地隔离该语句，但总而言之，诀窍是:

There's a lot more logic going on to isolate precisely the statement, but in short the trick is:

• 使用StackTrace检索源代码的位置和语句的行
• 解析源代码以获取确切的语句

当然，只有在用于编译代码的同一台计算机上运行它时，它才可以工作.

Of course, it can work only if you're running it on the same machine you used to compile the code.

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