RecursionTest

// Question posted at
//  https://www.facebook.com/groups/Javagroup123/permalink/10156805252566664/

import junit.framework.TestCase;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;

public class RecursionTest extends TestCase {

    public void test_0_and_0() {
        assertOutputEquals(new String[]{
                // No output at all.
        }, 0, 0);
    }

    public void test_0_and_10() {
        assertOutputEquals(new String[]{
                // No output at all.
        }, 0, 10);
    }

    public void test_1_of_1_only() {
        assertOutputEquals(new String[]{
                "1",
        }, 1, 1);
    }

    public void test_1_of_1_to_2() {
        assertOutputEquals(new String[]{
                "1",
                "2",
        }, 1, 2);
    }

    public void test_1_of_1_to_3() {
        assertOutputEquals(new String[]{
                "1",
                "2",
                "3",
        }, 1, 3);
    }

    public void test_1_of_1_to_5() {
        assertOutputEquals(new String[]{
                "1",
                "2",
                "3",
                "4",
                "5",
        }, 1, 5);
    }

    public void test_2_of_1_only() {
        assertOutputEquals(new String[]{
                "1 1",
        }, 2, 1);
    }

    public void test_2_of_1_to_2() {
        assertOutputEquals(new String[]{
                "1 1",
                "1 2",
                "2 2",
        }, 2, 2);
    }

    public void test_2_of_1_to_3() {
        assertOutputEquals(new String[]{
                "1 1",
                "1 2",
                "1 3",
                "2 2",
                "2 3",
                "3 3",
        }, 2, 3);
    }

    public void test_3_of_1_only() {
        assertOutputEquals(new String[]{
                "1 1 1",
        }, 3, 1);
    }

    public void test_5_of_1_only() {
        assertOutputEquals(new String[]{
                "1 1 1 1 1",
        }, 5, 1);
    }

    public void test_15_of_1_only() {
        assertOutputEquals(new String[]{
                "1 1 1 1 1 1 1 1 1 1 1 1 1 1 1",
        }, 15, 1);
    }

    public void test_3_of_1_to_2() {
        assertOutputEquals(new String[]{
                "1 1 1",
                "1 1 2",
                "1 2 2",
                "2 2 2",
        }, 3, 2);
    }

    public void test_3_of_1_to_3() {
        assertOutputEquals(new String[]{
                "1 1 1",
                "1 1 2",
                "1 1 3",
                "1 2 2",
                "1 2 3",
                "1 3 3",
                "2 2 2",
                "2 2 3",
                "2 3 3",
                "3 3 3",
        }, 3, 3);
    }

    public void test_10_and_0() {
        assertOutputEquals(new String[]{
                // No output at all.
        }, 10, 0);
    }

    private static final String NL = System.lineSeparator();

    private static void assertOutputEquals(final String[] expectedOutputLines, final int n, final int max) {
        final String actualOutput = callFunctionAndReturnStandardOutput(n, max);
        final String trimmedActualOutput = trimTrailingSpacesFromLines(actualOutput);

        final String expectedOutput = buildExpectedOutputString(expectedOutputLines);
        assertEquals(expectedOutput, trimmedActualOutput);
    }

    private static String callFunctionAndReturnStandardOutput(final int n, final int max) {
        final PrintStream oldSystemOut = System.out;
        final ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        final PrintStream printStream = new PrintStream(byteArrayOutputStream);
        System.setOut(printStream);
        try {

            // Function call being tested:
            Recursion.generateAndPrintValuesWithMax(n, max);

        } finally {
            System.setOut(oldSystemOut);
            printStream.close();
        }
        return byteArrayOutputStream.toString();
    }

    private static String trimTrailingSpacesFromLines(final String actualOutput) {
        final StringBuilder result = new StringBuilder();
        if (!"".equals(actualOutput)) {
            for (final String line : actualOutput.split(NL)) {
                result.append(line.replaceFirst("  *$", "")).append(NL);
            }
        }
        return result.toString();
    }

    private static String buildExpectedOutputString(String[] expectedOutputLines) {
        final StringBuilder expectedOutputStringBuilder = new StringBuilder();
        for (String line : expectedOutputLines) {
            expectedOutputStringBuilder.append(line);
            expectedOutputStringBuilder.append(NL);
        }
        return expectedOutputStringBuilder.toString();
    }

}