testData.apex

Pricebook2 pricebook = [SELECT Id FROM Pricebook2 WHERE IsStandard = TRUE LIMIT 1];

// Create customer account
Account account = new Account(
        Name = 'ORDER MANAGER TEST ACCOUNT',
        AccountNumber = 'TEST_ACCOUNT_NUMBER'
);
insert account;
// create contract
Contract contract = new Contract(
        AccountId = account.Id,
        Status = 'Draft',
        StartDate = Date.today(),
        ContractTerm = 24
);
insert contract;
contract.Status = 'Activated';
update contract;
// Create order
Order order = new Order(
        ContractId = contract.Id,
        Status = 'Draft',
        AccountId = account.Id,
        EffectiveDate = Date.today(),
        Pricebook2Id = pricebook.Id
);
insert order;
// create products
List<Product2> products = new List<Product2>();
for (Integer i = 0; i < 300; i++) {
    products.add(new Product2(
            Name = 'Product Test N°' + i,
            ProductCode = 'Product Code N°' + i,
            IsActive = true
    ));
}
insert products;
// create standard pricebook entries
Pricebook2 custom_pricebook = new Pricebook2(Name='TestPricebook', IsActive=true);
insert custom_pricebook;
List<PricebookEntry> pricebookEntries = new List<PricebookEntry>();
for (Product2 product : products) {
    pricebookEntries.add(
            new PricebookEntry(
                    Pricebook2Id = pricebook.Id,
                    Product2Id = product.Id,
                    UnitPrice = Math.random() * 1000,
                    IsActive = true
            )
    );
    pricebookEntries.add(
                new PricebookEntry(
                        Pricebook2Id = custom_pricebook.Id,
                        Product2Id = product.Id,
                        UnitPrice = Math.random() * 1000,
                        IsActive = true
                )
    );
}
insert pricebookEntries;
// create order items
List<OrderItem> orderItems = new List<OrderItem>();
for (PricebookEntry pricebookEntry: pricebookEntries) {
    if (pricebookEntry.UnitPrice>500) continue;
    orderItems.add(
            new OrderItem(
                    OrderId = order.Id,
                    UnitPrice = pricebookEntry.UnitPrice,
                    Quantity = Math.round(Math.random() * 99) + 1,
                    Product2Id = pricebookEntry.Product2Id,
                    PricebookEntryId = pricebookEntry.Id
            )
    );
}
insert orderItems;