Add tests for BuyTrade class

src/BuyTradeTest.java

+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class BuyTradeTest {
+
+	@Test
+	void buyTradeTest() {
+		Customer c = new Customer("c1");
+		BuyTrade buyTrade = new BuyTrade(1, c, 100, 200);
+		assertEquals(buyTrade.getCustomer().getId(), c.getId());
+		assertEquals(buyTrade.getPrice(), 200);
+		assertEquals(buyTrade.getQty(), 100);
+		assertEquals(buyTrade.getTime(), 1);
+		assertEquals(buyTrade.getType(), "BUY");
+	}
+
+}