模拟重载方法

Question

我正在使用scalamock来模拟一个包含一些重载方法的类，但我得到了一些错误。

例如:

val out = mock[PrintStream]
(out.print _).expects("cmd rn")

引发以下错误:

[error] [...]/src/test/scala/chili.scala:19: ambiguous reference to overloaded definition,
[error] both method print in class PrintStream of type (x$1: String)Unit
[error] and  method print in class PrintStream of type (x$1: Array[Char])Unit

但是如果我尝试使用:

(out.print(_: String)).expects("cmd rn")

我也得到一个错误:

[info] [...]/src/test/scala/chili.scala:19: Unable to resolve overloaded method print
[info]       (out.print(_: String)).expects("cmd rn")
[info]                 ^
[error] [...]/src/test/scala/chili.scala:19: value expects is not a member of String => Unit
[error]       (out.print(_: String)).expects("cmd rn")

有没有办法在scala中做到这一点?也许使用另一个库?

Answer 1

我相信您所看到的编译器错误与scalamock不能正确模拟PrintStream类的事实有关。如果查看scalamock scaladocs，您将看到以下语句:

At present, ScalaMock can only mock traits, Java interfaces, and non-final 
classes that define a default constructor

由于PrintStream类既不是接口也没有默认构造函数，我的猜测是scalamock不能正确地模拟它，您看到的错误是它的副作用。如果您将代码更改为使用OutputStream(这是一个接口，因此满足scalamock的限制)，则可以像这样执行重载方法mock:

val mockStream = mock[OutputStream]      
(mockStream.write(_:Int)) expects(1)
(mockStream.write(_:Array[Byte])) expects(Array[Byte](1,2,3))

就我个人而言，我更喜欢在Specs2中使用Mockito，因为它没有这些限制。一个使用PrintWriter的类的示例，然后使用Mockito模拟该类的测试规范如下:

import java.io.PrintStream
import java.io.File
import org.specs2.mutable.Specification
import org.specs2.mock.Mockito
class MockitoExample extends Specification with Mockito{
  val mockPrinter = mock[PrintStream]
  val myPrinter = new MyPrintingClass{
    override val printer = mockPrinter
  }
  "A request to print and attay of strings" should{
    "call println on the PrintStream for each string supplied" in {
      myPrinter print Array("foo", "bar")
      there was one(mockPrinter).println("foo")
      there was one(mockPrinter).println("bar")
    }
  }
}
class MyPrintingClass{
  val printer = new PrintStream(new File("foo.txt"))
  def print(strings:Array[String]) = strings foreach (printer.println(_))
}

现在这是一个非常简单的例子，只使用测试后验证，没有测试前的stub(因为println有一个Unit返回类型)，但至少你可以看到Mockito没有遭受与scalamock相同的限制。你可以阅读更多关于使用Mockito与Specs2在这里