accordant-operations

Operations in Accordant

An operation represents an atomic action your system can perform. Each operation has two parts:

• Apply: Describes what should happen (pure spec logic)
• Execute: Makes it actually happen (calls the real system)

Defining Operations

Inline Syntax

For simple specs, define operations inline:

var spec = new Spec<BankState>();

spec.Operation<string, ApiResult<decimal>>("CreateAccount", (accountId, state) =>
{
    // Apply logic here
    if (state.Accounts.ContainsKey(accountId))
        return Expect.That<ApiResult<decimal>>(r => r.IsConflict).SameState();

    return Expect.That<ApiResult<decimal>>(r => r.IsSuccess && r.Data == 0)
           .ThenState<BankState>(s => s.Accounts[accountId] = 0);
});

Binding Execution

Connect spec operations to real system calls:

spec.ExecuteWith<BankApiClient>()
    .Bind<string, ApiResult<decimal>>("CreateAccount",
        (client, accountId) => client.CreateAccount(accountId).Result)
    .Bind<(string, decimal), ApiResult<decimal>>("Withdraw",
        (client, req) => client.Withdraw(req.Item1, req.Item2).Result);

Class-Based Operations

For complex operations, use classes:

public class WithdrawOperation : Operation<WithdrawRequest, ApiResult<decimal>, BankState>
{
    public override ExpectedOutcomes Apply(WithdrawRequest request, BankState state)
    {
        if (!state.Accounts.TryGetValue(request.AccountId, out var balance))
            return Expect.That<ApiResult<decimal>>(r => r.IsNotFound).SameState();

        if (balance < request.Amount)
            return Expect.That<ApiResult<decimal>>(r => r.IsBadRequest).SameState();

        var newBalance = balance - request.Amount;
        return Expect.That<ApiResult<decimal>>(r => r.IsSuccess && r.Data == newBalance)
               .ThenState<BankState>(s => s.Accounts[request.AccountId] = newBalance);
    }

    public override async Task<ApiResult<decimal>> ExecuteAsync(
        WithdrawRequest request, 
        TestingContext context)
    {
        var client = context.Get<BankApiClient>();
        return await client.WithdrawAsync(request.AccountId, request.Amount);
    }
}