Change start command fixture to str

## Summary

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## Steps to Reproduce

[Outline the steps to consistently reproduce the issue.]

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## Expected Behavior

[Describe the expected result if the bug were resolved.]

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## Actual Behavior

[Describe what actually happens when the bug occurs.]

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## Logs/Errors

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JIRA Issue: BA-6785

Start by locating the start command fixture referenced in the title and inspect the tests that use it. Confirm the expected fixture type from those usages, change the fixture to a string, and run the affected tests to verify they pass.

Written by the indexing model from the issue text.