ring: test flake

[kevinburkesegment]

I just had a build fail due to a test failure in the ring package which I believe is unrelated to my changes, as I did not touch the ring package and the ring package doesn't import the packages I changed.

https://drone.grafana.net/grafana/dskit/3189/1/4

--- FAIL: TestSpreadMinimizingTokenGenerator_GetMissingTokens (7.29s)
    spread_minimizing_token_generator_test.go:476: 
        	Error Trace:	/drone/src/ring/spread_minimizing_token_generator_test.go:476
        	Error:      	"[%!s(uint32=2452015680) %!s(uint32=2476020736)]" should have 3 item(s), but has 2
        	Test:       	TestSpreadMinimizingTokenGenerator_GetMissingTokens
FAIL
FAIL	github.com/grafana/dskit/ring	260.251s

In addition it looks like the format string in the error generated by assert.Len is wrong; I raised stretchr/testify#1482 to try to fix that.

[charleskorn]

@duricanikolic knows the most about this test - would you mind taking a look?

[duricanikolic]

I will have a look at this and try to fix it.

[duricanikolic]

I have managed to reproduce the problem: as expected, in an unlucky case,

missingIndex := []int{rand.Intn(tokensPerInstance - 1), rand.Intn(tokensPerInstance - 1), rand.Intn(tokensPerInstance - 1)}

produces array with multiple occurrence of the same number, which caused the problem. I will now fix this.