# TestField Implementation Patterns

## Entry Point Validation
```al
procedure ProcessSalesOrder(var SalesHeader: Record "Sales Header")
begin
    // Validate prerequisites at procedure entry
    SalesHeader.TestField("Document Type", SalesHeader."Document Type"::Order);
    SalesHeader.TestField("Sell-to Customer No.");
    SalesHeader.TestField("Order Date");
    
    // Continue with business logic
    ProcessOrderLines(SalesHeader);
end;
```

## State-Dependent Validation
```al
procedure ReleasePurchaseDocument(var PurchaseHeader: Record "Purchase Header")
begin
    case PurchaseHeader."Document Type" of
        PurchaseHeader."Document Type"::Order:
            begin
                PurchaseHeader.TestField("Buy-from Vendor No.");
                PurchaseHeader.TestField("Expected Receipt Date");
            end;
        PurchaseHeader."Document Type"::Invoice:
            begin
                PurchaseHeader.TestField("Buy-from Vendor No.");
                PurchaseHeader.TestField("Posting Date");
            end;
    end;
end;
```

## Conditional Field Requirements
```al
trigger OnValidate()
begin
    if "Payment Method Code" <> '' then begin
        PaymentMethod.Get("Payment Method Code");
        if PaymentMethod."Bal. Account Type" = PaymentMethod."Bal. Account Type"::"Bank Account" then
            TestField("Bank Account No.");
    end;
end;
```

## Try Function Integration
```al
procedure TryValidateCustomerData(CustomerNo: Code[20]): Boolean
var
    Customer: Record Customer;
begin
    if not Customer.Get(CustomerNo) then
        exit(false);
        
    Customer.TestField(Name);
    Customer.TestField("Customer Posting Group");
    exit(true);
end;
```