feat: support data passing between [DependsOn] tests

[thomhurst]

Problem

When using [DependsOn] for workflow/sequential tests, there's no way to pass data from one test to the next. The current workaround is fragile static fields:

private static int _orderId; // fragile shared state

[Test]
public async Task Step1_Place_Order()
{
    var order = await CreateOrder();
    _orderId = order.Id; // side effect
}

[Test, DependsOn(nameof(Step1_Place_Order))]
public async Task Step2_Process_Payment()
{
    // Uses _orderId - but if Step1 failed, _orderId is 0
    await PayOrder(_orderId);
}

Problems with static fields:

• No type safety between producer and consumer
• Default values if predecessor fails (silent bugs)
• Not obvious which test produces which data
• Doesn't work well with parallel test classes

Proposed API

// Option A: Return value + parameter injection
[Test]
public async Task<int> Step1_Place_Order()
{
    var order = await CreateOrder();
    return order.Id; // explicit output
}

[Test, DependsOn(nameof(Step1_Place_Order))]
public async Task Step2_Process_Payment(
    [DependsOnResult(nameof(Step1_Place_Order))] int orderId)
{
    await PayOrder(orderId); // type-safe, injected
}

// Option B: TestContext-based state bag (simpler to implement)
[Test]
public async Task Step1_Place_Order(TestContext context)
{
    var order = await CreateOrder();
    context.SetResult(order.Id);
}

[Test, DependsOn(nameof(Step1_Place_Order))]
public async Task Step2_Process_Payment(TestContext context)
{
    var orderId = context.GetDependencyResult<int>(nameof(Step1_Place_Order));
}

Use Cases

• E2E workflow tests (create → process → verify)
• Setup chains where each step produces an ID/token/resource needed by the next
• Multi-step API interaction tests

Context

Discovered while building the CloudShop Aspire + TUnit example (#4761). The OrderWorkflowTests class needed a 4-step dependency chain sharing an order ID.

[claude]

Note: There is a current workaround available using TestContext.Dependencies.GetTests(...) as documented in #4048.

Example:

[Test]
public async Task Step1_Place_Order(TestContext context)
{
    var order = await CreateOrder();
    context.ObjectBag["orderId"] = order.Id; // Store in ObjectBag
}

[Test, DependsOn(nameof(Step1_Place_Order))]
public async Task Step2_Process_Payment(TestContext context)
{
    var dependency = context.Dependencies.GetTests(nameof(Step1_Place_Order)).First();
    var orderId = (int)dependency.ObjectBag["orderId"]; // Retrieve from dependency's ObjectBag
}

However, this feature request proposes a more ergonomic, type-safe API which would be a significant DX improvement.

[thomhurst]

Closing - this is already supported via TestContext.StateBag and TestContext.Dependencies. Example:

[Test]
public async Task Step1_Place_Order()
{
    var order = await CreateOrder();
    TestContext.Current!.StateBag.Items["OrderId"] = order.Id;
}

[Test, DependsOn(nameof(Step1_Place_Order))]
public async Task Step2_Process_Payment()
{
    var firstTest = TestContext.Current!.Dependencies.GetTests(nameof(Step1_Place_Order))[0];
    var orderId = (int)firstTest.StateBag.Items["OrderId"];
    await PayOrder(orderId);
}

See TUnit.TestProject/Bugs/3627/Tests.cs for the full example. The CloudShop example will be updated to use this pattern.