Add Yieldlab Adapter

[mirkorean]

New Adapter for Yieldlab (https://www.yieldlab.com)

Test Parameters:
https://github.com/prebid/Prebid.js/blob/master/modules/yieldlabBidAdapter.md

[x] Official
Contact: solutions@yieldlab.de

[guscarreon]

@mirkorean thank you for submitting your adapter. I'm the first reviewer and can tell your adapter looks pretty solid. I have some feedback on the source code and in the test case front, where we try to keep the coverage above 90%, I believe a couple more test cases to cover some more scenarios in adapters/yieldlabyieldlab.go

╭─ ~/go/src/github.com/prebid/prebid-server/adapters/yieldlab  ‹PR1287›
╰─➤  go test -coverprofile=c.out
PASS
coverage: 83.4% of statements
ok      github.com/prebid/prebid-server/adapters/yieldlab       0.035s
╭─ ~/go/src/github.com/prebid/prebid-server/adapters/yieldlab  ‹PR1287*›
╰─➤  go tool cover -func=c.out
github.com/prebid/prebid-server/adapters/yieldlab/usersync.go:10:       NewYieldlabSyncer       100.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:28:       NewYieldlabBidder       0.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:37:       MakeRequests            100.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:51:       makeEndpointURL         86.7%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:101:      getGDPR                 85.7%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:125:      makeTargetingValues     100.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:133:      makeRequest             84.2%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:170:      parseRequest            80.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:194:      mergeParams             100.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:212:      MakeBids                77.8%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:281:      findBidReq              80.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:292:      makeBannerAdSource      100.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:296:      makeAdSourceURL         100.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:315:      makeCreativeID          100.0%
github.com/prebid/prebid-server/adapters/yieldlab/yieldlab.go:319:      splitSize               70.0%
total:                                                                  (statements)            85.1%

[mirkorean]

Thank you for the review @guscarreon! Much Appreciated! I'll let @aklinkert respond to your comments as he did all the work on the adapter.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[SyntaxNode]

Commenting to remove the stale label while we're waiting on @aklinkert.

[aklinkert]

@guscarreon @mirkorean I updated the code (rebased on current master) and modified it to reflect the suggestions by @guscarreon.

Regarding coverage: I did some lower hanging fruits to increase the test coverage, anything else would result in unjustified increase in amount of test code. I looked through the coverage report, all uncovered lines are now error handling cases and IMHO do not need to be tested explicitly. We now have a coverage of 87.4% and by thus are in the upper third, looking though the other adapters coverage.

[guscarreon]

LGTM

[aklinkert]

@SyntaxNode Are we able to merge this PR? Or is there anything left that needs a second glance? :)

[guscarreon]

LGTM