[TEST] Improve body parser test coverage

[asos-craigmorten]

Issue

The current body-parser test coverage is low, this issue seeks to improve the coverage.

Details

The Opine body-parser test code was written prior to the creation of SuperDeno and thus was unpractical at the time to port test code from the original source. Now the supertest equivalent exists we should look to improve the test coverage of these modules.

Test files:

• ./test/units/bodyParser.json.test.ts
• ./test/units/bodyParser.raw.test.ts
• ./test/units/bodyParser.text.test.ts
• ./test/units/bodyParser.urlencoded.test.ts

See https://github.com/expressjs/body-parser for details, specifically https://github.com/expressjs/body-parser/tree/master/test for guidance on desired coverage.