Made a test class and tested code

src/main/java/amanidrummond/CarRental.java

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+package amanidrummond;
+
+public class CarRental {
+
+    private String customerName;
+    private String carModel;
+    private int rentalDays;
+    private double dailyRate;
+    private boolean luxury;
+
+    public CarRental(String customerName, String carModel, int rentalDays, double dailyRate, boolean luxury) {
+        if (rentalDays <= 0) {
+            throw new IllegalArgumentException("Rental days must be greater than 0");
+        }
+        if (dailyRate <= 0) {
+            throw new IllegalArgumentException("Daily rate must be greater than 0");
+        }
+
+        this.customerName = customerName;
+        this.carModel = carModel;
+        this.rentalDays = rentalDays;
+        this.dailyRate = dailyRate;
+        this.luxury = luxury;
+    }
+
+    public String getCustomerName() {
+        return customerName;
+    }
+
+    public void setCustomerName(String customerName) {
+        this.customerName = customerName;
+    }
+
+    public String getCarModel() {
+        return carModel;
+    }
+
+    public void setCarModel(String carModel) {
+        this.carModel = carModel;
+    }
+
+    public int getRentalDays() {
+        return rentalDays;
+    }
+
+    public void setRentalDays(int rentalDays) {
+        if (rentalDays <= 0) {
+            throw new IllegalArgumentException("Rental days must be greater than 0");
+        }
+        this.rentalDays = rentalDays;
+    }
+
+    public double getDailyRate() {
+        return dailyRate;
+    }
+
+    public void setDailyRate(double dailyRate) {
+        if (dailyRate <= 0) {
+            throw new IllegalArgumentException("Daily rate must be greater than 0");
+        }
+        this.dailyRate = dailyRate;
+    }
+
+    public boolean isLuxury() {
+        return luxury;
+    }
+
+    public void setLuxury(boolean luxury) {
+        this.luxury = luxury;
+    }
+
+    public double calculateTotalCost() {
+        double total = rentalDays * dailyRate;
+        if (luxury) {
+            total += 100;
+        }
+        return total;
+    }
+
+    public boolean qualifiesForDiscount() {
+        return rentalDays >= 7;
+    }
+}

src/test/java/amanidrummond/test/CarRental.java

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+package amanidrummond.test;
+
+import amanidrummond.CarRental;
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class CarRentalTest {
+
+    @Test
+    void constructorHappyPath() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "Toyota Camry", 5, 40.0, false);
+
+        // Act / Assert
+        assertEquals("Alex", rental.getCustomerName());
+        assertEquals("Toyota Camry", rental.getCarModel());
+        assertEquals(5, rental.getRentalDays());
+        assertEquals(40.0, rental.getDailyRate());
+        assertFalse(rental.isLuxury());
+    }
+
+    @Test
+    void constructorThrowsWhenRentalDaysIsZero() {
+        // Arrange / Act / Assert
+        assertThrows(IllegalArgumentException.class, () -> {
+            new CarRental("Alex", "Toyota Camry", 0, 40.0, false);
+        });
+    }
+
+    @Test
+    void constructorThrowsWhenDailyRateIsZero() {
+        // Arrange / Act / Assert
+        assertThrows(IllegalArgumentException.class, () -> {
+            new CarRental("Alex", "Toyota Camry", 5, 0, false);
+        });
+    }
+
+    @Test
+    void settersAndGettersWork() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "Toyota Camry", 5, 40.0, false);
+
+        // Act
+        rental.setCustomerName("Jordan");
+        rental.setCarModel("Honda Civic");
+        rental.setRentalDays(10);
+        rental.setDailyRate(55.0);
+        rental.setLuxury(true);
+
+        // Assert
+        assertEquals("Jordan", rental.getCustomerName());
+        assertEquals("Honda Civic", rental.getCarModel());
+        assertEquals(10, rental.getRentalDays());
+        assertEquals(55.0, rental.getDailyRate());
+        assertTrue(rental.isLuxury());
+    }
+
+    @Test
+    void setRentalDaysThrowsForNegativeValue() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "Toyota Camry", 5, 40.0, false);
+
+        // Act / Assert
+        assertThrows(IllegalArgumentException.class, () -> {
+            rental.setRentalDays(-2);
+        });
+    }
+
+    @Test
+    void setDailyRateThrowsForNegativeValue() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "Toyota Camry", 5, 40.0, false);
+
+        // Act / Assert
+        assertThrows(IllegalArgumentException.class, () -> {
+            rental.setDailyRate(-10.0);
+        });
+    }
+
+    @Test
+    void calculateTotalCostWithoutLuxuryFee() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "Toyota Camry", 5, 40.0, false);
+
+        // Act
+        double total = rental.calculateTotalCost();
+
+        // Assert
+        assertEquals(200.0, total);
+    }
+
+    @Test
+    void calculateTotalCostWithLuxuryFee() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "BMW 7 Series", 3, 100.0, true);
+
+        // Act
+        double total = rental.calculateTotalCost();
+
+        // Assert
+        assertEquals(400.0, total);
+    }
+
+    @Test
+    void qualifiesForDiscountReturnsTrueWhenRentalDaysIsSevenOrMore() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "Toyota Camry", 7, 40.0, false);
+
+        // Act
+        boolean result = rental.qualifiesForDiscount();
+
+        // Assert
+        assertTrue(result);
+    }
+
+    @Test
+    void qualifiesForDiscountReturnsFalseWhenRentalDaysIsLessThanSeven() {
+        // Arrange
+        CarRental rental = new CarRental("Alex", "Toyota Camry", 3, 40.0, false);
+
+        // Act
+        boolean result = rental.qualifiesForDiscount();
+
+        // Assert
+        assertFalse(result);
+    }
+}