#1317 Special Case Pattern (#1624)

* #1317 Add Special Case Pattern

To focus on pattern itself, I implement DB and
maintenance lock by the singleton instance.

* #1317 Add special cases unit tests

Assert the logger output
(ref: https://stackoverflow.com/a/52229629)

* #1317 Add README.md

Add Special Case Pattern README

* #1317 Format: add a new line to end of file

Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>

special-case/src/test/java/com/iluwatar/specialcase/AppTest.java

@@ -0,0 +1,16 @@
+package com.iluwatar.specialcase;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Application test.
+ */
+public class AppTest {
+
+  @Test
+  void shouldExecuteWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}

special-case/src/test/java/com/iluwatar/specialcase/SpecialCasesTest.java

@@ -0,0 +1,120 @@
+package com.iluwatar.specialcase;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.slf4j.LoggerFactory;
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.read.ListAppender;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeEach;
+
+/**
+ * Special cases unit tests. (including the successful scenario {@link ReceiptDto})
+ */
+public class SpecialCasesTest {
+  private static ApplicationServices applicationServices;
+  private static ReceiptViewModel receipt;
+
+  @BeforeAll
+  static void beforeAll() {
+    Db.getInstance().seedUser("ignite1771", 1000.0);
+    Db.getInstance().seedItem("computer", 800.0);
+    Db.getInstance().seedItem("car", 20000.0);
+
+    applicationServices = new ApplicationServicesImpl();
+  }
+
+  @BeforeEach
+  public void beforeEach() {
+    MaintenanceLock.getInstance().setLock(false);
+  }
+
+  @Test
+  public void testDownForMaintenance() {
+    final Logger LOGGER = (Logger) LoggerFactory.getLogger(DownForMaintenance.class);
+
+    ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
+    listAppender.start();
+    LOGGER.addAppender(listAppender);
+
+    MaintenanceLock.getInstance().setLock(true);
+    receipt = applicationServices.loggedInUserPurchase(null, null);
+    receipt.show();
+
+    List<ILoggingEvent> loggingEventList = listAppender.list;
+    assertEquals("Down for maintenance", loggingEventList.get(0).getMessage());
+    assertEquals(Level.INFO, loggingEventList.get(0).getLevel());
+  }
+
+  @Test
+  public void testInvalidUser() {
+    final Logger LOGGER = (Logger) LoggerFactory.getLogger(InvalidUser.class);
+
+    ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
+    listAppender.start();
+    LOGGER.addAppender(listAppender);
+
+    receipt = applicationServices.loggedInUserPurchase("a", null);
+    receipt.show();
+
+    List<ILoggingEvent> loggingEventList = listAppender.list;
+    assertEquals("Invalid user: a", loggingEventList.get(0).getMessage());
+    assertEquals(Level.INFO, loggingEventList.get(0).getLevel());
+  }
+
+  @Test
+  public void testOutOfStock() {
+    final Logger LOGGER = (Logger) LoggerFactory.getLogger(OutOfStock.class);
+
+    ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
+    listAppender.start();
+    LOGGER.addAppender(listAppender);
+
+    receipt = applicationServices.loggedInUserPurchase("ignite1771", "tv");
+    receipt.show();
+
+    List<ILoggingEvent> loggingEventList = listAppender.list;
+    assertEquals("Out of stock: tv for user = ignite1771 to buy"
+        , loggingEventList.get(0).getMessage());
+    assertEquals(Level.INFO, loggingEventList.get(0).getLevel());
+  }
+
+  @Test
+  public void testInsufficientFunds() {
+    final Logger LOGGER = (Logger) LoggerFactory.getLogger(InsufficientFunds.class);
+
+    ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
+    listAppender.start();
+    LOGGER.addAppender(listAppender);
+
+    receipt = applicationServices.loggedInUserPurchase("ignite1771", "car");
+    receipt.show();
+
+    List<ILoggingEvent> loggingEventList = listAppender.list;
+    assertEquals("Insufficient funds: 1000.0 of user: ignite1771 for buying item: car"
+        , loggingEventList.get(0).getMessage());
+    assertEquals(Level.INFO, loggingEventList.get(0).getLevel());
+  }
+
+  @Test
+  public void testReceiptDto() {
+    final Logger LOGGER = (Logger) LoggerFactory.getLogger(ReceiptDto.class);
+
+    ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
+    listAppender.start();
+    LOGGER.addAppender(listAppender);
+
+    receipt = applicationServices.loggedInUserPurchase("ignite1771", "computer");
+    receipt.show();
+
+    List<ILoggingEvent> loggingEventList = listAppender.list;
+    assertEquals("Receipt: 800.0 paid"
+        , loggingEventList.get(0).getMessage());
+    assertEquals(Level.INFO, loggingEventList.get(0).getLevel());
+  }
+}