Unit testing text output (stdout.write/print) in Dart - unit-testing

Question

I am looking for a way in the Dart programming language to redirect the
output from stdout, into a "Something", that I can call .toString() on, and get
anything printed on stdout as String. This is useful for unit tests.
Currently I wrap stdout in my Display class, and store the text for one call and verify that stdout's write is
used. See also my side note below, how it can be done in Java.
import 'dart:io';
import 'package:mockito/mockito.dart';
import 'package:test/test.dart';
class Display {
IOSink output;
String lastTextPrinted;
Display(IOSink output) {
this.output = output;
}
void myPrint(String text) {
lastTextPrinted = text;
output.write(text);
}
}
main() {
test('prints hello world', () {
Display display = new Display(stdout);
display.myPrint("Hello world!");
expect("Hello world!", display.lastTextPrinted);
});
test('myPrint calls ioSinks write', () {
MockIOSink ioSink = new MockIOSink();
Display display = Display(ioSink);
display.myPrint("Hello world!");
verify(ioSink.write("Hello world!"));
});
}
class MockIOSink extends Mock implements IOSink {}
Sidenote: In Java with JUnit 4 I used something similar to this:
There System.out is a PrintStream and I can assign my own Stream to it, for instance ByteArrayOutPutStream.
The latter has a .toString method I can call to verify its content against.
#Test
public void testMyMessageToDisplay() throws Exception
{
ByteArrayOutputStream canvas = new ByteArrayOutputStream();
System.setOut(new PrintStream(canvas);
new Display().displayMyMessage("Hello world!");
Assert.assertEquals("Hello World!", canvas.toString("UTF-8"));
}
public static class Display {
public void displayMyMessage(String myMessage) {
System.out.println(myMessage);
}
}

Answer 1

Look at https://pub.dartlang.org/packages/test_process – it gives a lot of nice methods for verifying the output of a process
See the example in the readme:
import 'package:test/test.dart';
import 'package:test_process/test_process.dart';
void main() {
test("pub get gets dependencies", () async {
var process = await TestProcess.start("pub", ["get"]);
// Each stream matcher will consume as many lines as it matches from a
// StreamQueue, and no more, so it's safe to use them in sequence.
await expectLater(process.stdout, emits("Resolving dependencies..."));
// The emitsThrough matcher matches and consumes any number of lines, as
// long as they end with one matching the argument.
await expectLater(process.stdout, emitsThrough("Got dependencies!"));
await process.shouldExit(0);
});
}