test: adding ShareTest

src/test/java/millions/ShareTest.java

@@ -2,4 +2,33 @@
 
 import static org.junit.jupiter.api.Assertions.*;
 
-class ShareTest {}
+import java.math.BigDecimal;
+import org.junit.jupiter.api.Test;
+
+class ShareTest {
+
+  @Test
+  public void testHappyPath() {
+    Stock stock = new Stock("AYO", "Ayhoo", BigDecimal.valueOf(10));
+    Share share = new Share(stock, 5, BigDecimal.valueOf(10));
+    assertEquals(BigDecimal.valueOf(5), share.getQuantity());
+  }
+
+  @Test
+  public void testGetters() {
+    Stock stock = new Stock("AYO", "Ayhoo", BigDecimal.valueOf(10));
+    Share share = new Share(stock, 5, BigDecimal.valueOf(10));
+    assertEquals(BigDecimal.valueOf(5), share.getQuantity());
+    assertEquals(stock, share.getStock());
+    assertEquals(BigDecimal.valueOf(10), share.getPurchasePrice());
+  }
+
+  @Test
+  public void testNullsAndInvalid() {
+    Stock stock = new Stock("AYO", "Ayhoo", BigDecimal.valueOf(10));
+    assertThrows(IllegalArgumentException.class, () -> new Share(null, 2, BigDecimal.valueOf(2)));
+    assertThrows(IllegalArgumentException.class, () -> new Share(stock, 2, null));
+    assertThrows(
+        IllegalArgumentException.class, () -> new Share(stock, null, BigDecimal.valueOf(2)));
+  }
+}