tests: replaced stretchr/testify by go-openapi/testify

[fredbi]

Change type

Please select: 🆕 New feature or enhancement|🔧 Bug fix'|📃 Documentation update

Short description

Fixes

Full description

Checklist

• I have signed all my commits with my name and email (see DCO. This does not require a PGP-signed commit
• I have rebased and squashed my work, so only one commit remains
• I have added tests to cover my changes.
• I have properly enriched go doc comments in code.
• I have properly documented any breaking change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.01%. Comparing base (b93d88e) to head (75f5aa1).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #182   +/-   ##
=======================================
  Coverage   85.01%   85.01%           
=======================================
  Files          14       14           
  Lines        2015     2015           
=======================================
  Hits         1713     1713           
  Misses        218      218           
  Partials       84       84           

Flag	Coverage Δ
oldstable-macos-latest	85.01% <ø> (ø)
oldstable-ubuntu-latest	85.01% <ø> (ø)
oldstable-windows-latest	85.01% <ø> (ø)
stable-macos-latest	85.01% <ø> (ø)
stable-ubuntu-latest	85.01% <ø> (ø)
stable-windows-latest	85.01% <ø> (ø)

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