[Prometheus Receiver ] Modify existing test to validate core metric types

[PaurushGarg]

Is your feature request related to a problem? Please describe.
Problem Statement:
The existing test checks for core metric types (gauge, counter, histogram, and summary) and their values. The validation part of this test is skipped because this test has been failing due to insertion of staleness markers.
See:

opentelemetry-collector-contrib/receiver/prometheusreceiver/metrics_receiver_test.go

Line 1442 in 9ceb2ff

if true {

Current Behavior
The current behavior shows that if the validation is re-enabled the tests fail at the AssertUp due to failed scrapes, as the test falsely assume that staleness markers will not be returned. The functionality to make this test work after inclusion of staleness markers needs to be added.

Describe the solution you'd like
We propose the following solution

Modify the existing test to add a method to filter out the failed scrapes in the function getValidScrapes :

opentelemetry-collector-contrib/receiver/prometheusreceiver/metrics_receiver_test.go

Line 202 in 9ceb2ff

func getValidScrapes(t *testing.T, mds []*agentmetricspb.ExportMetricsServiceRequest) []*agentmetricspb.ExportMetricsServiceRequest {

Result Expected: Once this filter is added, all Prometheus metric types will be validated.

We’d like to get feedback on alternative solutions so please comment on this issue.

Additional context
Related to: open-telemetry/wg-prometheus#57
cc: @alolita @Aneurysm9

[PaurushGarg]

@alolita please assign this issue to me. I would like to work on this one.

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