# Testing and debugging durable functions
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Testing and debugging durable functions locally works similarly to regular Lambda functions, with automatic support for checkpointing and replay. This guide covers common testing scenarios and troubleshooting techniques.

## Local testing workflow
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When testing durable functions locally, the workflow differs from regular Lambda functions:

**Durable function testing workflow**

1. Build your application:

   ```
   $ sam build
   ```

1. Invoke your durable function:

   ```
   $ sam local invoke MyDurableFunction --durable-execution-name test 
   ```

1. Check execution history if needed:

   ```
   $ sam local execution history execution-id
   ```

## Common testing scenarios
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### Testing checkpointing behavior
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To test that your function properly checkpoints state:

```
# Example Python durable function
def handler(event, context):
    # This will create a checkpoint
    context.wait(10)  # Wait 10 seconds
    
    # Function resumes here after wait
    return {"message": "Function resumed after wait"}
```

When you invoke this function locally, the wait period is handled automatically.

### Testing callback scenarios
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For functions that wait for external callbacks:

1. Start your durable function that waits for a callback

1. In another terminal, resolve the callback:

   ```
   $ sam local callback succeed callback-id
   ```

1. Observe the function resume execution

## Troubleshooting
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### Durable function not executing properly
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**Problem:** The function doesn't behave as a durable function.

**Solutions:**
+ Verify that `DurableConfig` is set in your SAM template
+ Ensure your function code uses durable function SDK methods (e.g., `context.wait()`)
+ Check that you're using a supported runtime (TypeScript, JavaScript, Python)

### Cannot retrieve execution history
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**Problem:** The `local execution history` command returns no results.

**Solutions:**
+ Verify the execution ID is correct
+ Check that the function has been invoked at least once

### Callback commands not working
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**Problem:** Callback commands don't resolve pending operations.

**Solutions:**
+ Verify the callback ID is correct
+ Ensure the function is actually waiting for a callback
+ Verify you're using the correct callback command syntax

## Debugging tips
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+ **Use execution history** - Review execution history to understand the flow of your durable function
+ **Test incrementally** - Start with simple wait operations before adding complex logic
+ **Use verbose logging** - Enable detailed logging to trace execution flow

## Learn more
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For more information about testing and debugging, see:
+ [Introduction to testing with sam local invoke](using-sam-cli-local-invoke.md) - Local invoke documentation
+ [sam local execution history](sam-cli-command-reference-sam-local-execution-history.md) - Execution history