Adding System.exit example

core-java-modules/core-java-os/src/test/java/com/baeldung/system/exit/SystemExitUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.system.exit;
+
+import static org.junit.Assert.assertEquals;
+
+import java.security.Permission;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+public class SystemExitUnitTest {
+
+    protected static class ExitException extends SecurityException {
+
+        private static final long serialVersionUID = 1L;
+        public final int status;
+
+        public ExitException(int status) {
+            this.status = status;
+        }
+    }
+
+    private static class NoExitSecurityManager extends SecurityManager {
+        @Override
+        public void checkPermission(Permission perm) {
+        }
+
+        @Override
+        public void checkPermission(Permission perm, Object context) {
+        }
+
+        @Override
+        public void checkExit(int status) {
+            super.checkExit(status);
+            throw new ExitException(status);
+        }
+    }
+
+    private SecurityManager securityManager;
+
+    private SystemExitExample example;
+
+    @Before
+    public void setUp() throws Exception {
+        example = new SystemExitExample();
+        securityManager = System.getSecurityManager();
+        System.setSecurityManager(new NoExitSecurityManager());
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        System.setSecurityManager(securityManager);
+    }
+
+    @Test
+    public void testExit() throws Exception {
+        try {
+            example.readFile();
+        } catch (ExitException e) {
+            assertEquals("Exit status", 2, e.status);
+        }
+    }
+}