implemented and added test cases for DB dao. Added dependency of Hierarchical junit runner in parent pom

dao/src/test/java/com/iluwatar/dao/DBCustomerDaoTest.java

@@ -0,0 +1,149 @@
+package com.iluwatar.dao;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assume.assumeTrue;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.stream.Stream;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import de.bechte.junit.runners.context.HierarchicalContextRunner;
+
+@RunWith(HierarchicalContextRunner.class)
+public class DBCustomerDaoTest {
+  
+  private static final String DB_URL = "jdbc:h2:~/dao:customerdb";
+  private DBCustomerDao dao;
+  private Customer existingCustomer = new Customer(1, "Freddy", "Krueger");
+
+  @Before
+  public void createSchema() throws SQLException {
+    try (Connection connection = DriverManager.getConnection(DB_URL);
+        Statement statement = connection.createStatement()) {
+      statement.execute("CREATE TABLE CUSTOMERS (ID NUMBER, FNAME VARCHAR(100), LNAME VARCHAR(100))");
+    }
+  }
+  
+  @Before
+  public void setUp() {
+    dao = new DBCustomerDao(DB_URL);
+    boolean result = dao.add(existingCustomer);
+    assumeTrue(result);
+  }
+  
+  public class NonExistantCustomer {
+    
+    @Test
+    public void addingShouldResultInSuccess() {
+      try (Stream<Customer> allCustomers = dao.getAll()) {
+        assumeTrue(allCustomers.count() == 1);
+      }
+      
+      final Customer nonExistingCustomer = new Customer(2, "Robert", "Englund");
+      boolean result = dao.add(nonExistingCustomer);
+      assertTrue(result);
+      
+      assertCustomerCountIs(2);
+      assertEquals(nonExistingCustomer, dao.getById(nonExistingCustomer.getId()));
+    }
+    
+    @Test
+    public void deletionShouldBeFailureAndNotAffectExistingCustomers() {
+      final Customer nonExistingCustomer = new Customer(2, "Robert", "Englund");
+      boolean result = dao.delete(nonExistingCustomer);
+      
+      assertFalse(result);
+      assertCustomerCountIs(1);
+    }
+    
+    @Test
+    public void updationShouldBeFailureAndNotAffectExistingCustomers() {
+      final int nonExistingId = getNonExistingCustomerId();
+      final String newFirstname = "Douglas";
+      final String newLastname = "MacArthur";
+      final Customer customer = new Customer(nonExistingId, newFirstname, newLastname);
+      boolean result = dao.update(customer);
+      
+      assertFalse(result);
+      assertNull(dao.getById(nonExistingId));
+    }
+    
+    @Test
+    public void retrieveShouldReturnNull() {
+      assertNull(dao.getById(getNonExistingCustomerId()));
+    }
+    
+  }
+  
+  public class ExistingCustomer {
+    
+    @Test
+    public void addingShouldResultInFailureAndNotAffectExistingCustomers() {
+      Customer existingCustomer = new Customer(1, "Freddy", "Krueger");
+      
+      boolean result = dao.add(existingCustomer);
+      
+      assertFalse(result);
+      assertCustomerCountIs(1);
+      assertEquals(existingCustomer, dao.getById(existingCustomer.getId()));
+    }
+    
+    @Test
+    public void deletionShouldBeSuccessAndCustomerShouldBeNonAccessible() {
+      boolean result = dao.delete(existingCustomer);
+      
+      assertTrue(result);
+      assertCustomerCountIs(0);
+      assertNull(dao.getById(existingCustomer.getId()));
+    }
+    
+    @Test
+    public void updationShouldBeSuccessAndAccessingTheSameCustomerShouldReturnUpdatedInformation() {
+      final String newFirstname = "Bernard";
+      final String newLastname = "Montgomery";
+      final Customer customer = new Customer(existingCustomer.getId(), newFirstname, newLastname);
+      boolean result = dao.update(customer);
+      
+      assertTrue(result);
+      
+      final Customer cust = dao.getById(existingCustomer.getId());
+      assertEquals(newFirstname, cust.getFirstName());
+      assertEquals(newLastname, cust.getLastName());
+    }
+    
+  }
+
+  @After
+  public void deleteSchema() throws SQLException {
+    try (Connection connection = DriverManager.getConnection(DB_URL);
+        Statement statement = connection.createStatement()) {
+      statement.execute("DROP TABLE CUSTOMERS");
+    }
+  }
+  
+  private void assertCustomerCountIs(int count) {
+    try (Stream<Customer> allCustomers = dao.getAll()) {
+      assertTrue(allCustomers.count() == count);
+    }
+  }
+  
+
+  /**
+   * An arbitrary number which does not correspond to an active Customer id.
+   * 
+   * @return an int of a customer id which doesn't exist
+   */
+  private int getNonExistingCustomerId() {
+    return 999;
+  }
+}