BAEL-6585 - Unit Testing of System.in with JUnit (#14436)

* BAEL-6585 - Unit Testing of System.in with JUnit

* Rename test classes

* Remane test classes

testing-modules/testing-libraries-2/src/main/java/com/baeldung/systemin/Application.java

@@ -0,0 +1,17 @@
+package com.baeldung.systemin;
+
+import java.util.Scanner;
+
+public class Application {
+
+    public static final String NAME = "Name: ";
+
+    private Application() {
+    }
+
+    public static String readName() {
+        Scanner scanner = new Scanner(System.in);
+        String input = scanner.next();
+        return NAME.concat(input);
+    }
+}

testing-modules/testing-libraries-2/src/test/java/com/baeldung/systemin/SystemInUnitTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.systemin;
+
+import com.github.stefanbirkner.systemlambda.SystemLambda;
+import org.junit.jupiter.api.Test;
+import uk.org.webcompere.systemstubs.SystemStubs;
+
+import java.io.ByteArrayInputStream;
+
+import static com.baeldung.systemin.Application.NAME;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class SystemInUnitTest {
+    private void provideInput(String data) {
+        ByteArrayInputStream testIn = new ByteArrayInputStream(data.getBytes());
+        System.setIn(testIn);
+    }
+
+    @Test
+    void givenName_whenReadNameFromInput_thenReturnCorrectResult() {
+        provideInput("Baeldung");
+        String input = Application.readName();
+        assertEquals(NAME.concat("Baeldung"), input);
+    }
+
+    @Test
+    void givenName_whenReadWithSystemLambda_thenReturnCorrectResult() throws Exception {
+        SystemLambda.withTextFromSystemIn("Baeldung")
+                .execute(() -> assertEquals(NAME.concat("Baeldung"), Application.readName()));
+    }
+
+    @Test
+    void givenName_whenReadWithSystemStubs_thenReturnCorrectResult() throws Exception {
+        SystemStubs.withTextFromSystemIn("Baeldung")
+                .execute(() -> {
+                    assertThat(Application.readName())
+                            .isEqualTo(NAME.concat("Baeldung"));
+                });
+    }
+}

testing-modules/testing-libraries-2/src/test/java/com/baeldung/systemin/SystemRulesUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.systemin;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.contrib.java.lang.system.TextFromStandardInputStream;
+
+import static com.baeldung.systemin.Application.NAME;
+import static org.junit.Assert.assertEquals;
+import static org.junit.contrib.java.lang.system.TextFromStandardInputStream.emptyStandardInputStream;
+
+public class SystemRulesUnitTest {
+
+    @Rule
+    public final TextFromStandardInputStream systemIn = emptyStandardInputStream();
+
+    @Test
+    public void givenName_whenReadWithSystemRules_thenReturnCorrectResult() {
+        systemIn.provideLines("Baeldung");
+        assertEquals(NAME.concat("Baeldung"), Application.readName());
+    }
+}
+

testing-modules/testing-libraries-2/src/test/java/com/baeldung/systemin/SystemStubsUnitTest.java

@@ -0,0 +1,19 @@
+package com.baeldung.systemin;
+
+import org.junit.Rule;
+import org.junit.Test;
+import uk.org.webcompere.systemstubs.rules.SystemInRule;
+
+import static com.baeldung.systemin.Application.NAME;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class SystemStubsUnitTest {
+
+    @Rule
+    public SystemInRule systemInRule = new SystemInRule("Baeldung");
+
+    @Test
+    public void givenName_whenReadWithSystemStubs_thenReturnCorrectResult() {
+        assertThat(Application.readName()).isEqualTo(NAME.concat("Baeldung"));
+    }
+}