scala Scalatest - 如何测试 println
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Scalatest - how to test println
提问by Luigi Plinge
Is there something in Scalatest that will allow me to test the output to the standard out via a printlnstatement?
Scalatest 中有什么东西可以让我通过println语句测试输出到标准输出吗？
So far I've mainly been using FunSuite with ShouldMatchers.
到目前为止，我主要使用FunSuite with ShouldMatchers.
e.g. how do we check the printed output of
例如，我们如何检查打印输出
object Hi {
def hello() {
println("hello world")
}
}
采纳答案by Eric
The usual way to test print statements on the console is to structure your program a bit differently so that you can intercept those statements. You can for example introduce an Outputtrait:
在控制台上测试打印语句的常用方法是稍微不同地构建您的程序，以便您可以拦截这些语句。例如，您可以引入一个Output特征：
trait Output {
def print(s: String) = Console.println(s)
}
class Hi extends Output {
def hello() = print("hello world")
}
And in your tests you can define another trait MockOutputactually intercepting the calls:
在您的测试中，您可以定义另一个MockOutput实际拦截调用的特征：
trait MockOutput extends Output {
var messages: Seq[String] = Seq()
override def print(s: String) = messages = messages :+ s
}
val hi = new Hi with MockOutput
hi.hello()
hi.messages should contain("hello world")
回答by Kevin Wright
If you just want to redirect console output for a limited duration, use the withOutand withErrmethods defined on Console:
如果您只想在有限的时间内重定向控制台输出，请使用withOut和 上withErr定义的方法Console：
val stream = new java.io.ByteArrayOutputStream()
Console.withOut(stream) {
//all printlns in this block will be redirected
println("Fly me to the moon, let me play among the stars")
}
回答by Matthew Farwell
You can replace where println writes to by using Console.setOut(PrintStream)
您可以使用 Console.setOut(PrintStream) 替换 println 写入的位置
val stream = new java.io.ByteArrayOutputStream()
Console.setOut(stream)
println("Hello world")
Console.err.println(stream.toByteArray)
Console.err.println(stream.toString)
You can obviously use any type of stream you want. You can do the same sort of thing for stderr and stdin with
显然，您可以使用任何类型的流。你可以对 stderr 和 stdin 做同样的事情
Console.setErr(PrintStream)
Console.setIn(PrintStream)
