JUnit test for System.out.println()

Question

I need to write JUnit tests for an old application that\'s poorly designed and is writing a lot of error messages to standard output. When the getResponse(String reque

Answer 1

Full JUnit 5 example to test System.out (replace the when part):

package learning;

import static org.assertj.core.api.BDDAssertions.then;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

class SystemOutLT {

    private PrintStream originalSystemOut;
    private ByteArrayOutputStream systemOutContent;

    @BeforeEach
    void redirectSystemOutStream() {

        originalSystemOut = System.out;

        // given
        systemOutContent = new ByteArrayOutputStream();
        System.setOut(new PrintStream(systemOutContent));
    }

    @AfterEach
    void restoreSystemOutStream() {
        System.setOut(originalSystemOut);
    }

    @Test
    void shouldPrintToSystemOut() {

        // when
        System.out.println("example");

        then(systemOutContent.toString()).containsIgnoringCase("example");
    }
}