Closes #93: Mobile assertion bails out early and passes after desktop assertion fails

[jeawhanlee]

Description

This PR fixes the issue where mobile assertion bails out because failMsg state retention from previous scenario(desktop)

Fixes #93

Documentation

User documentation

Explain how this code impacts users.

Technical documentation

The code resets the failMsg variable, setting it to an empty string in the preceding step.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue).

New dependencies

List any new dependencies that are required for this change.

Risks

None

Checklists

Feature validation

• [ ] I validated all the Acceptance Criteria. If possible, provide sreenshots or videos.
• [x] I triggered all changed lines of code at least once without new errors/warnings/notices.
• [ ] I implemented built-in tests to cover the new/changed code.

Documentation

• [ ] I prepared the user documentation for the feature/enhancement and shared it in the PR or the GitHub issue.
• [ ] The user documentation covers new/changed entry points (endpoints, WP hooks, configuration files, ...).
• [ ] I prepared the technical documentation if needed, and shared it in the PR or the GitHub issue.

Code style

• [ ] I wrote self-explanatory code about what it does.
• [ ] I wrote comments to explain why it does it.
• [ ] I named variables and functions explicitely.
• [ ] I protected entry points against unexpected inputs.
• [ ] I did not introduce unecessary complexity.
• [ ] I listed the introduced external dependencies explicitely on the PR.
• [ ] I validated the repo-specific guidelines from CONTRIBUTING.md.

Observability

• [ ] I handled errors when needed.
• [ ] I wrote user-facing messages that are understandable and provide actionable feedbacks.
• [ ] I prepared ways to observe the implemented system (logs, data, etc.).

Risks

• [ ] I explicitely mentioned performance risks in the PR.
• [ ] I explicitely mentioned security risks in the PR.