BAEL-5959: Monad in Java (#13278)

* BAEL-5959: Monad in Java

* Fix test name

core-java-modules/core-java-8/src/test/java/com/baeldung/monad/MonadSampleUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.monad;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class MonadSampleUnitTest {
+
+    @Test
+    public void whenNotUsingMonad_shouldBeOk() {
+        MonadSample1 test = new MonadSample1();
+        Assert.assertEquals(6.0, test.apply(2), 0.000);
+    }
+
+    @Test
+    public void whenNotUsingMonadButUsingTempVars_shouldBeOk() {
+        MonadSample2 test = new MonadSample2();
+        Assert.assertEquals(6.0, test.apply(2), 0.000);
+    }
+
+    @Test
+    public void whenUsingMonad_shouldBeOk() {
+        MonadSample3 test = new MonadSample3();
+        Assert.assertEquals(6.0, test.apply(2), 0.000);
+    }
+
+    @Test
+    public void whenTestingMonadProperties_shouldBeOk() {
+        MonadSample4 test = new MonadSample4();
+        Assert.assertEquals(true, test.leftIdentity());
+        Assert.assertEquals(true, test.rightIdentity());
+        Assert.assertEquals(true, test.associativity());
+    }
+
+    @Test
+    public void whenBreakingMonadProperties_shouldBeFalse() {
+        MonadSample5 test = new MonadSample5();
+        Assert.assertEquals(false, test.fail());
+    }
+}