fix: raise MQTTError with message instead of class itself

[reachsridhard]

PR: fix: raise MQTTError with message instead of class itself

Description

This PR fixes a bug in MQTTClient.__enter__ where exceptions.MQTTError was raised without creating an exception instance.

Previously, when the client failed to connect to the MQTT broker within the configured timeout, Python attempted to raise the exception class itself rather than an instance. This resulted in a confusing TypeError instead of a meaningful MQTT connection error.

---

Problem

In client.py, the original implementation contained:

raise exceptions.MQTTError

Raising the exception class directly is incorrect because MQTTError expects an error message.

Instead of reporting the actual connection timeout, users would receive a misleading traceback caused by Python attempting to instantiate the exception without the required arguments.

This behavior was also inconsistent with every other MQTTError usage in the same file, where descriptive messages are always provided:

raise exceptions.MQTTError("could not publish message") from e

raise exceptions.MQTTError(
    "err {:s}: {:s}".format(...)
)

raise exceptions.MQTTError(
    f"Error subscribing to '{topic}' (err code {status})"
)

This was the only call site raising the exception incorrectly.

---

Changes

Updated client.py to raise an MQTTError instance with a descriptive timeout message.

Before

self._disconnect()
logger.error(
    "Could not connect to broker after %s seconds",
    self._connect_timeout,
)
raise exceptions.MQTTError

After

self._disconnect()
logger.error(
    "Could not connect to broker after %s seconds",
    self._connect_timeout,
)
raise exceptions.MQTTError(
    "Could not connect to broker after {} seconds".format(
        self._connect_timeout
    )
)

---

Fix

The fix replaces the invalid class-only raise with a properly instantiated MQTTError, including the configured timeout value in the error message.

This provides users with a clear and actionable exception while maintaining consistency with the rest of the MQTT error handling in the file.

---

Testing

• Existing MQTT integration tests already exercise the connection workflow.
• This change only affects the error path when MQTTClient.__enter__ times out waiting for the broker.

---

[coderabbitai]

📝 Walkthrough

Walkthrough

MQTTClient.__enter__ now raises MQTTError with the configured timeout when the broker connection is not established in time.

Changes

MQTT timeout handling

Layer / File(s)	Summary
Report connection timeout tavern/_plugins/mqtt/client.py	The timeout failure raises MQTTError with a formatted message that includes the configured timeout.

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: raising an MQTTError instance with a message instead of the exception class.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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