test: Adding SaleTest

src/test/java/millions/SaleTest.java

@@ -2,4 +2,31 @@
 
 import static org.junit.jupiter.api.Assertions.*;
 
-class SaleTest {}
+import java.math.BigDecimal;
+import org.junit.jupiter.api.Test;
+
+class SaleTest {
+
+  @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));
+    player.getPortfolio().addShare(share);
+    Sale sale = new Sale(share, 1);
+    sale.commit(player);
+    assertTrue(sale.isCommitted());
+
+    assertEquals(120, player.getMoney().intValue());
+    assertFalse(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));
+    Sale sale = new Sale(share, 1);
+    assertThrows(IllegalStateException.class, () -> sale.commit(player));
+  }
+}