BAEL-4341 - JUnit test for System.out.println()

testing-modules/testing-libraries/pom.xml

@@ -42,7 +42,18 @@
             <artifactId>spring-boot-starter-web</artifactId>
             <version>2.2.0.RELEASE</version>
         </dependency>
-
+        <dependency>
+            <groupId>com.github.stefanbirkner</groupId>
+            <artifactId>system-rules</artifactId>
+            <version>${system-rules.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.github.stefanbirkner</groupId>
+            <artifactId>system-lambda</artifactId>
+            <version>${system-lambda.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -90,6 +101,8 @@
         <lambda-behave.version>0.4</lambda-behave.version>
         <cucumber.version>4.8.0</cucumber.version>
         <checkstyle-maven-plugin.version>3.0.0</checkstyle-maven-plugin.version>
+        <system-rules.version>1.19.0</system-rules.version>
+        <system-lambda.version>1.0.0</system-lambda.version>
     </properties>
 
 </project>

testing-modules/testing-libraries/src/test/java/com/baeldung/systemout/SystemOutPrintlnUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.systemout;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+
+import org.junit.Assert;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static com.github.stefanbirkner.systemlambda.SystemLambda.tapSystemOut;
+
+class SystemOutPrintlnUnitTest {
+
+    private final ByteArrayOutputStream outputStreamCaptor = new ByteArrayOutputStream();
+    private final PrintStream standardOut = System.out;
+
+    @BeforeEach
+    public void setUp() {
+        System.setOut(new PrintStream(outputStreamCaptor));
+    }
+
+    @BeforeEach
+    public void tearDown() {
+        System.setOut(standardOut);
+    }
+
+    @Test
+    void givenSystemOutRedirection_whenInvokePrintln_thenOutputCaptorSuccess() {
+        print("Hello Baeldung Readers!!");
+
+        Assert.assertEquals("Hello Baeldung Readers!!", outputStreamCaptor.toString()
+            .trim());
+    }
+
+    @Test
+    void givenTapSystemOut_whenInvokePrintln_thenOutputIsReturnedSuccessfully() throws Exception {
+
+        String text = tapSystemOut(() -> {
+            print("Hello Baeldung Readers!!");
+        });
+
+        Assert.assertEquals("Hello Baeldung Readers!!", text.trim());
+    }
+
+    private void print(String output) {
+        System.out.println(output);
+    }
+
+}

testing-modules/testing-libraries/src/test/java/com/baeldung/systemout/SystemOutPrintlnWithRuleUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.systemout;
+
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.contrib.java.lang.system.SystemOutRule;
+
+public class SystemOutPrintlnWithRuleUnitTest {
+
+    @Rule
+    public final SystemOutRule systemOutRule = new SystemOutRule().enableLog();
+
+    @Test
+    public void givenSystemOutRule_whenInvokePrintln_thenLogSuccess() {
+        print("Hello Baeldung Readers!!");
+
+        Assert.assertEquals("Hello Baeldung Readers!!", systemOutRule.getLog()
+            .trim());
+
+        Assert.assertEquals("Hello Baeldung Readers!!\n", systemOutRule.getLogWithNormalizedLineSeparator());
+    }
+
+    private void print(String output) {
+        System.out.println(output);
+    }
+
+}