Added diff report tests

[mjjimenez]

Description

Adds model diff report tests (part of feature tests here: #122 )

Checklist

• I have followed the Contribution Guidelines and Code of Conduct
• I have commented my code following the OpenMined Styleguide
• I have labeled this PR with the relevant Type labels
• My changes are covered by tests

[codecov]

Codecov Report

Merging #154 into master will increase coverage by 0.69%.
The diff coverage is 82.92%.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
+ Coverage   52.49%   53.19%   +0.69%     
==========================================
  Files          16       16              
  Lines        1861     1861              
==========================================
+ Hits          977      990      +13     
+ Misses        884      871      -13     

Impacted Files	Coverage Δ
SwiftSyft/Classes/APIPayload.swift	78.78% <ø> (ø)
SwiftSyft/Classes/SyftPlan.swift	7.54% <ø> (ø)
SwiftSyft/Classes/SyftRTCClient.swift	0.00% <0.00%> (ø)
SwiftSyft/Classes/NetworkManager.swift	73.07% <75.00%> (ø)
SwiftSyft/Classes/PingChecker.swift	81.25% <75.00%> (ø)
SwiftSyft/Classes/SyftClient.swift	80.92% <91.66%> (+5.23%)	⬆️
SwiftSyft/Classes/DownloadService.swift	75.86% <100.00%> (-13.80%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 25d5874...3ba1e9b. Read the comment docs.