fix(tests): Fix race condition causing flakiness in PHP generator test

[cpcallen]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide
• I ran npm run format and npm run lint

The details

Resolves

Turns out process.exit() was sometimes getting called before the (async) fs.writeFile had finished writing the last of the generator output files. This was causing occasional failures where the last (or last several) generator tests would fail because they ended up writing 0 byte files.

Proposed Changes

Use fs.writeFileSync instead of fs.writeFile

Behaviour Before Change

Generator tests could fail due to a race condition.

Behaviour After Change

Generator tests no longer fail because of this particular race condition.

Reason for Changes

Changes made in one of my TS-related branches were causing this failure to happen almost every time.