End-to-end tests for gomod binary

[Helcaraxan]

Feature request

Checklist

• The feature / improvement you are suggesting overlaps with the purpose of gomod:
  facilitating the management of Go modules and their dependencies.
• You have examined various alternatives to the new feature / improvement you are suggesting
  and are describing the results in the description below.
• You have filled in the three sections below and deleted their corresponding placeholders
  texts.

Description

The gomod binary (mostly the main package) needs to be tested appropriately and achieve adequate (>80%) code coverage.

Implementation suggestions

Reuse the test harness created for the lib/modules package to inject content and test specific outcome.

Additional information

N.A.