test: Adding PurchaseTest

src/test/java/millions/PurchaseTest.java

@@ -2,4 +2,39 @@
 
 import static org.junit.jupiter.api.Assertions.*;
 
-class PurchaseTest {}
+import java.math.BigDecimal;
+import org.junit.jupiter.api.Test;
+
+class PurchaseTest {
+  @Test
+  public void testHappyPath() {
+    Stock stock = new Stock("TestStock", "TST", BigDecimal.valueOf(10));
+    Share share = new Share(stock, 2, BigDecimal.valueOf(10));
+    Player player = new Player("TestPlayer", BigDecimal.valueOf(100));
+    Purchase purchase = new Purchase(share, 1);
+    purchase.commit(player);
+    assertTrue(purchase.isCommitted());
+
+    // 1 less because of tax
+    assertEquals(79, player.getMoney().intValue());
+    assertTrue(player.getPortfolio().getShares().contains(share));
+  }
+
+  @Test
+  public void testNullsAndInvalid() {
+
+    Stock stock = new Stock("TestStock", "TST", BigDecimal.valueOf(10));
+    Share share = new Share(stock, 2, BigDecimal.valueOf(10));
+    Player player = new Player("TestPlayer", BigDecimal.valueOf(100));
+    Purchase purchase = new Purchase(share, 1);
+
+    // Double commit
+    purchase.commit(player);
+    assertThrows(IllegalStateException.class, () -> purchase.commit(player));
+
+    // Insufficient funds
+    Player poorPlayer = new Player("PoorPlayer", BigDecimal.valueOf(10));
+    Purchase expensivePurchase = new Purchase(new Share(stock, 20, BigDecimal.valueOf(10)), 1);
+    assertThrows(IllegalStateException.class, () -> expensivePurchase.commit(poorPlayer));
+  }
+}