Show coverage report in HTML format

[jjngx]

Proposed changes

Add a make target make cover-html for running tests with coverage and displaying reports in HTML format in local browser. When test execution is completed test coverage report is automatically opened in default web browser.

Example:

➜  kubernetes-ingress git:(local-coverage-check) make cover-html
go test -shuffle=on -race ./... -count=1 -cover -covermode=atomic -coverprofile=coverage.out
ok  	github.com/nginxinc/kubernetes-ingress/cmd/nginx-ingress	2.535s	coverage: 6.8% of statements
ok  	github.com/nginxinc/kubernetes-ingress/internal/configs	1.873s	coverage: 66.6% of statements
[...]
go tool cover -html coverage.out

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork

[ciarams87]

👍🏼