race: make code coverage + data race detection default for tests

[henvic]

Is your feature request related to a problem? Please describe.
Most likely not, but perhaps I might've identified the opportunity to improve this due to a bug (unsure).

Describe the solution you'd like
I want developers to learn about running Go tests with code coverage and data race detector sooner. This means better libraries and programs will be written in the long run because developers will find issues earlier (i.e., understanding when and how to use mutex).

A simple solution might be just to change the default -covermode from 'set' to 'atomic'.

Describe alternatives you've considered
Given that such a change makes running tests a magnitude slower, it might be seen as a bad thing. An extra button close to "run tests | debug tests" on top of the testing functions (when editing test files) might be to add something like a "run test with code coverage and -race" option there too.

On the Go extension settings panel, we might be able to choose to use it by default. In this case, the options might end up as something like this:

run tests | debug tests | fast

Where fast would be the same as executing a vanilla go test -run=TestFoo$.

Additional context
I only noticed this issue after updating go to 1.15.2 and VS Code to 1.49.1 + latest Go extension as of today. Previously, everything seemed to be working smoothly. I haven't investigated how or why.

• By everything I mean data race detection + code coverage.

[hyangah]

@henvic thanks for the feature request + bug report.
@pjweinbgo I think "go.coverMode" should default to an empty so go test should find the right mode.

[gopherbot]

Change https://golang.org/cl/256117 mentions this issue: package.json: default 'go.coverMode' to be empty

[gopherbot]

Change https://golang.org/cl/257602 mentions this issue: [release] package.json: default 'go.coverMode' to be 'default'