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Application development - Testing

Temporal provides a framework to facilitate Workflow and integration testing.

Replay​

Replay recreates the exact state of a Workflow Execution. You can replay a Workflow from the beginning of its history when resumed.

Replay allows code to resume only if it is compatible from a deterministic point of view.

To retrieve the Workflow History, use any of the following options and then pass the object to your SDK of choice.

Use the worker.WorflowReplayer to replay an existing Workflow Execution from its Event History to replicate errors.

For example, the following code retrieves the Event History of a Workflow:

import (
    "context"

    "go.temporal.io/api/enums/v1"
    "go.temporal.io/api/history/v1"
    "go.temporal.io/sdk/client"
)

func GetWorkflowHistory(ctx context.Context, client client.Client, id, runID string) (*history.History, error) {
    var hist history.History
    iter := client.GetWorkflowHistory(ctx, id, runID, false, enums.HISTORY_EVENT_FILTER_TYPE_ALL_EVENT)
    for iter.HasNext() {
        event, err := iter.Next()
        if err != nil {
            return nil, err
        }
        hist.Events = append(hist.Events, event)
    }
    return &hist, nil
}

This history can then be used to replay. For example, the following code creates a WorkflowReplayer and register the YourWorkflow Workflow function. Then it calls the ReplayWorkflowHistory to replay the Event History and return an error code.

import (
    "context"

    "go.temporal.io/sdk/client"
    "go.temporal.io/sdk/worker"
)

func ReplayWorkflow(ctx context.Context, client client.Client, id, runID string) error {
    hist, err := GetWorkflowHistory(ctx, client, id, runID)
    if err != nil {
        return err
    }
    replayer := worker.NewWorkflowReplayer()
    replayer.RegisterWorkflow(YourWorkflow)
    return replayer.ReplayWorkflowHistory(nil, hist)
}

The code above will cause the Worker to re-execute the Workflow's Workflow Function using the original Event History. If a noticeably different code path was followed or some code caused a deadlock, it will be returned in the error code. Replaying a Workflow Execution locally is a good way to see exactly what code path was taken for given input and events.