A very basic test exists and was slightly improved in #2936.
Opening an issue to improve test coverage to make sure the spec requirements are validated : https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#metricreader

Current tests only trigger the collect for both readers simultaneously. It need not be that way, so additional tests needed to cover this test gap.

The SDK MUST support multiple MetricReader instances to be registered on the same MeterProvider, and the MetricReader.Collect invocation on one MetricReader instance SHOULD NOT introduce side-effects to other MetricReader instances. For example, if a MetricReader instance is receiving metric data points that have delta temporality, it is expected that SDK will update the time range - e.g. from (Tn, Tn+1] to (Tn+1, Tn+2] - ONLY for this particular MetricReader instance.