delphi - 如何模拟日期和现在？

Question

我的一些代码使用Date and Now。因此，对该代码执行测试的结果取决于执行时间。那当然是不好的。
那么在测试中建议使用伪造日期和时间的推荐方式是什么？

使用界面？

Answer 1

为了使事物可测试，您需要在代码中具有或创建seams。

在此特定示例中，您可能希望使用环境上下文设计模式来实现此目的。虽然起初看起来像单例，但实际上允许临时替换使用的实例或返回的数据。下面是一个示例，说明如何基于this blog post在Delphi中实现它。

我省略了线程安全性和所有其他内容，以向您提供它如何工作的基本概念。您可能还完全摆脱了TDateTimeProvider单例/类，而只是制作了自己的与模仿配合使用的Now函数。

program AmbientContextDemo;

uses
  Generics.Collections,
  TestFramework,
  TestInsight.DUnit,
  System.SysUtils;

type
  TDateTimeProvider = class
  strict private
    class var fInstance: TDateTimeProvider;
    class function GetInstance: TDateTimeProvider; static;
  public
    function Now: TDateTime;
    class property Instance: TDateTimeProvider read GetInstance;
  end;

  TDateTimeProviderContext = class
  strict private
    var fContextNow: TDateTime;
    class var contextStack: TStack<TDateTimeProviderContext>;
    class function GetCurrent: TDateTimeProviderContext; static;
  public
    class constructor Create;
    class destructor Destroy;

    constructor Create(const contextNow: TDateTime);
    destructor Destroy; override;

    property ContextNow: TDateTime read fContextNow;
    class property Current: TDateTimeProviderContext read GetCurrent;
  end;

  TStuff = class
    // class procedure for demo purpose, no instance necessary in test
    class function DoSomeDateTimeStuff_UsingNow: TDateTime;
    class function DoSomeDateTimeStuff_UsingAmbientContext: TDateTime;
  end;

  TMyTest = class(TTestCase)
  published
    procedure TestIt_Fail;
    procedure TestIt_Pass;
  end;

{ TDateTimeProvider }

class function TDateTimeProvider.GetInstance: TDateTimeProvider;
begin
  if not Assigned(fInstance) then
    fInstance := TDateTimeProvider.Create;
  Result := fInstance;
end;

function TDateTimeProvider.Now: TDateTime;
var
  context: TDateTimeProviderContext;
begin
  context := TDateTimeProviderContext.Current;
  if Assigned(context) then
    Result := context.ContextNow
  else
    Result := System.SysUtils.Now;
end;

{ TMyTest }

procedure TMyTest.TestIt_Fail;
begin
  CheckEquals(EncodeDate(2018, 11, 11), TStuff.DoSomeDateTimeStuff_UsingNow);
end;

procedure TMyTest.TestIt_Pass;
var
  ctx: TDateTimeProviderContext;
begin
  ctx := TDateTimeProviderContext.Create(EncodeDate(2018, 11, 11));
  try
    CheckEquals(EncodeDate(2018, 11, 11), TStuff.DoSomeDateTimeStuff_UsingAmbientContext);
  finally
    ctx.Free;
  end;
end;

{ TStuff }

class function TStuff.DoSomeDateTimeStuff_UsingNow: TDateTime;
begin
  Result := Now; // using Now which is unmockable, only via hooking but that affects all occurences even in the RTL
end;

class function TStuff.DoSomeDateTimeStuff_UsingAmbientContext: TDateTime;
begin
  Result := TDateTimeProvider.Instance.Now;
end;

{ TDateTimeProviderContext }

class constructor TDateTimeProviderContext.Create;
begin
  contextStack := TStack<TDateTimeProviderContext>.Create;
end;

class destructor TDateTimeProviderContext.Destroy;
begin
  contextStack.Free;
end;

constructor TDateTimeProviderContext.Create(const contextNow: TDateTime);
begin
  fContextNow := contextNow;
  contextStack.Push(Self);
end;

destructor TDateTimeProviderContext.Destroy;
begin
  contextStack.Pop;
end;

class function TDateTimeProviderContext.GetCurrent: TDateTimeProviderContext;
begin
  if contextStack.Count = 0 then
    Result := nil
  else
    Result := contextStack.Peek;
end;

begin
  RegisterTest(TMyTest.Suite);
  RunRegisteredTests;
end.