Improve coverage

[thomaspoignant]

Description

Coverage went down since the mono repo.
This PR add some tests to improve it.

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have followed the contributing guide

[netlify]

✅ Deploy Preview for go-feature-flag-doc-preview canceled.

Name	Link
🔨 Latest commit	561a2c4
🔍 Latest deploy log	https://app.netlify.com/sites/go-feature-flag-doc-preview/deploys/6415d4fe9a0ddc0008835e98

[codecov]

Codecov Report

Merging #571 (561a2c4) into main (74c7d39) will increase coverage by 0.88%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #571      +/-   ##
==========================================
+ Coverage   86.70%   87.58%   +0.88%     
==========================================
  Files          54       57       +3     
  Lines        2505     2570      +65     
==========================================
+ Hits         2172     2251      +79     
+ Misses        281      271      -10     
+ Partials       52       48       -4     

Impacted Files	Coverage Δ
cmd/migrationcli/main.go	19.35% <ø> (ø)
exporter/fileexporter/exporter.go	92.85% <100.00%> (ø)
exporter/logsexporter/exporter.go	85.71% <100.00%> (ø)
exporter/webhookexporter/exporter.go	93.61% <100.00%> (ø)
retriever/fileretriever/retriever.go	100.00% <100.00%> (ø)

... and 7 files with indirect coverage changes

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication