Added unit testing sample code

Author: ravidsrk

README.md

@@ -40,6 +40,84 @@ Complete reference for Android Testing with examples.
 ## Local
 
 ### JUnit basics
+
+```java
+public class Calculator {
+
+    public int add(int op1, int op2) {
+        return op1 + op2;
+    }
+
+    public int diff(int op1, int op2) {
+        return op1 - op2;
+    }
+
+    public double div(int op1, int op2) {
+        // if (op2 == 0) return 0;
+        return op1 / op2;
+    }
+}
+
+// Unit tests
+public class CalculatorTest {
+
+    private Calculator calculator;
+
+    @Before
+    public void setup() {
+        calculator = new Calculator();
+        System.out.println("Ready for testing!");
+    }
+
+    @After
+    public void cleanup() {
+        System.out.println("Done with unit test!");
+    }
+
+    @BeforeClass
+    public static void testClassSetup() {
+        System.out.println("Getting test class ready");
+    }
+
+    @AfterClass
+    public static void testClassCleanup() {
+        System.out.println("Done with tests");
+    }
+
+    @Test
+    public void testAdd() {
+        calculator = new Calculator();
+        int total = calculator.add(4, 5);
+        assertEquals("Calculator is not adding correctly", 9, total);
+    }
+
+    @Test
+    public void testDiff() {
+        calculator = new Calculator();
+        int total = calculator.diff(9, 2);
+        assertEquals("Calculator is not subtracting correctly", 7, total);
+    }
+
+    @Test
+    public void testDiv() {
+        calculator = new Calculator();
+        double total = calculator.div(9, 3);
+        assertEquals("Calculator is not dividing correctly", 3.0, total, 0.0);
+    }
+
+    @Ignore
+    @Test(expected = java.lang.ArithmeticException.class)
+    public void testDivWithZeroDivisor() {
+        calculator = new Calculator();
+        double total = calculator.div(9, 0);
+        assertEquals("Calculator is not handling division by zero correctly", 0.0, total, 0.0);
+    }
+}
+
+```
+
+
+
 ### Beyond JUnit basics
 ### Local test setup and execution
 ### Adding local tests and failure