rpcserver: add handleTicketFeeInfo tests.

[dnldd]

depends on #2407

This adds rpc tests for handleTicketFeeInfo.

Work towards #2069.

[dnldd]

go tool cover -func=cov.out | grep -E handleTicketFeeInfo
github.com/decred/dcrd/internal/rpcserver/rpcserver.go:4881:              handleTicketFeeInfo             97.2%

Having some difficulty hitting this, pointers appreciated.

[rstaudt2]

go tool cover -func=cov.out | grep -E handleTicketFeeInfo
github.com/decred/dcrd/internal/rpcserver/rpcserver.go:4881:              handleTicketFeeInfo             97.2%

Having some difficulty hitting this, pointers appreciated.

You can stub any of the functions called in ticketFeeInfoForRange to return an err to hit that case. For example:

mockChain: func() *testRPCChain {
	chain := defaultMockRPCChain()
	chain.heightRangeErr = errors.New("")
	return chain
}(),

It's probably worth getting test coverage on the ticketFeeInfoForRange function as well.

[dnldd]

Needed to make the heightRange field a function to facilitate mocking it to fail on the second call.

go tool cover -func=cov.out | grep -E handleTicketFeeInfo
github.com/decred/dcrd/internal/rpcserver/rpcserver.go:4881:            handleTicketFeeInfo           100.0%

[davecgh]

This looks ready to me.

@rstaudt2 Is all of your feedback addressed?