SupplySystem with test before refactoring

// BEFORE REFACTORING:


package org.legacy;

import org.junit.Before;
import org.junit.Test;
import org.mockito.Mockito;

public class SupplyMonitorTest {
    private SupplyMonitor underTest;
    private Inventory inventory = Mockito.mock(Inventory.class);

    @Before
    public void setUp() throws Exception {
        underTest = new SupplyMonitor(inventory, 100);
    }

    @Test
    public void should_order_pencils_when_undersupplied() {
        Mockito.when(inventory.getItemCount(SupplyMonitor.PENCIL_ITEM_CODE)).thenReturn(120);
        underTest.trackAndProcurePencils();

        // Oh, dear. Not only to I have no way to test what happened inside the
        // method under test, but I think I just bought 280 pencils with my credit card!!!!
    }
}

//-------------------------------------------------------

package org.legacy;

public class SupplyMonitor {
    private static final int TARGET_PENCILS_PER_EMPLOYEE = 4;
    static final String PENCIL_ITEM_CODE = "123";
    private static final String CREDIT_CARD_NUMBER = "XXXX XXXX XXXX XXXX";

    private Inventory inventory;
    private int currentEmployeeCount;

    public SupplyMonitor(Inventory inventory, int currentEmployeeCount) {
        super();
        this.inventory = inventory;
        this.currentEmployeeCount = currentEmployeeCount;
    }

    public void trackAndProcurePencils() {
        int targetPencilCount = this.currentEmployeeCount * TARGET_PENCILS_PER_EMPLOYEE;
        int currentPencilCount = inventory.getItemCount(PENCIL_ITEM_CODE);
        if (currentPencilCount < targetPencilCount) {
            SupplySystem.buy(new PurchaseOrder(PENCIL_ITEM_CODE, targetPencilCount - currentPencilCount),
                    new CreditCard(CREDIT_CARD_NUMBER));
        }
    }

}