Unit Testing Prometheus Alerts

I have been writing unit tests for my Prometheus alerts and I have just increased the interval range in my alert, therefore I need to modify my current test. This is my modified test:

      - interval: 15m
        # Series data.
          - series: 'some_bucket{service_name="some-service", le="1000"}'
            values: 6 6 6 6 6 6 6
          - series: 'some_bucket{service_name="some-service", le="10000"}'
            values: 10 11 12 13 14 14 14
          - series: 'some_bucket{service_name="some-service", le="+Inf"}'
            values: 10 100 200 300 400 500 600
          - eval_time: 5m
            alertname: someName
            exp_alerts: []
          - eval_time: 15m
            alertname: someName
              - exp_labels:
                  severity: error
                  service_name: some-service
                  summary: "a summary"
                  description: "adescription"

and my alert rule is:

histogram_quantile(0.95, sum by(le) (rate(some_bucket{service_name="some-service"}[15m]))) >= 1000

The test is working fine, it does not trigger at the eval_time of 5 minutes and it does when it hits the correct interval. My question is regarding the interval set at the top

    - interval: 15m

My understanding is that this should be the scraping interval, but if I change it to 1 the test fails. Why is that? Does it mean that my time series/input data needs changing? Can you help me navigate the expected values for the input series?

Thank you