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Version: ZIO 2.x


TestConsole allows testing of applications that interact with the console by modeling working with standard input and output as writing and reading to and from internal buffers:

import zio._
import zio.test.{test, _}
import zio.test.Assertion._

val consoleSuite = suite("ConsoleTest")(
test("One can test output of console") {
for {
_ <- TestConsole.feedLines("Jimmy", "37")
_ <- Console.printLine("What is your name?")
name <- Console.readLine
_ <- Console.printLine("What is your age?")
age <-
questionVector <- TestConsole.output
q1 = questionVector(0)
q2 = questionVector(1)
} yield {
assertTrue(name == "Jimmy") &&
assertTrue(age == 37) &&
assertTrue(q1 == "What is your name?\n") &&
assertTrue(q2 == "What is your age?\n")

The above code simulates an application that will ask for the name and age of the user. To test it we prefill buffers with answers with the call to TestConsole.feedLines method. Calls to Console.readLine will get the value from the buffers instead of interacting with the users keyboard.

Also, all output that our program produces by calling Console.printLine (and other printing methods) is being gathered and can be accessed with a call to TestConsole.output.

TestConsole provides a testable interface for programs interacting with the console by modeling input and output as reading from and writing to input and output buffers maintained by TestConsole and backed by a Ref.

All calls to print and printLine using the TestConsole will write the string to the output buffer and all calls to readLine will take a string from the input buffer.

To facilitate debugging, by default output will also be rendered to standard output. We can enable or disable this for a scope using debug, silent, or the corresponding test aspects.

TestConsole has several methods to access and manipulate the content of these buffers including:

  • feedLines to feed strings to the input buffer that will then be returned by calls to readLine.
  • output to get the content of the output buffer from calls to print and printLine
  • clearInput and clearOutput to clear the respective buffers.

Together, these functions make it easy to test programs interacting with the console.