Extra data expected in alert unit test

Prometheus server
1

I’m seeing something strange when I unit test a disk space alert. The output from promtool is:

$ ./promtool test rules testalertrules.yml
Unit Testing:  testalertrules.yml
  FAILED:
    alertname:DiskSpace20%Free, time:3m,
        exp:"[Labels:{alertname=\"DiskSpace20%Free\", instance=\"rfmfxevnt-vp1:9100\", mountpoint=\"/\", severity=\"moderate\"} Annotations:{}, Labels:{alertname=\"DiskSpace20%Free\"} Annotations:{description=\"Diskspace on rfmfxevnt-vp1:9100 filesystem / has 19% available.\"}]",
        got:"[Labels:{alertname=\"DiskSpace20%Free\", instance=\"rfmfxevnt-vp1:9100\", mountpoint=\"/\", severity=\"moderate\"} Annotations:{description=\"Diskspace on rfmfxevnt-vp1:9100 filesystem / has 19% available.\"}]"

Note that the expected alert has an extra 'Annotations:{}, Labels:{alertname=“DiskSpace20%Free”} ’ If I remove that they match up perfectly. Since the Annotations and Labels are already expected, how am I generating these extra requirements?

------------------------------- alertrules.yml ------------------------------------

groups:
  - name: disk_space
    rules:

    - alert: DiskSpace20%Free
      expr: 100 - round(100 * node_filesystem_avail_bytes / node_filesystem_size_bytes) < 20
      labels:
        severity: moderate
      annotations:
        description: "Diskspace on {{ $labels.instance }} filesystem {{ $labels.mountpoint }} has {{ $value }}% available."

------------------------------- testalertrules.yml ------------------------------------

rule_files:
  - alertrules.yml

evaluation_interval: 1m

tests:
  # Series data
  - interval: 1m
    input_series:
        # 30% 27% 25% 19% 15% 11% 9% 5% 30%
      - series: 'node_filesystem_size_bytes{instance="rfmfxevnt-vp1:9100", mountpoint="/"}'
        values: '10726932480 10726932480 10726932480 10726932480'
      - series: 'node_filesystem_avail_bytes{instance="rfmfxevnt-vp1:9100", mountpoint="/"}'
        values: '7508852736 7830660710 8045199360 8688815308'

    alert_rule_test:
      - alertname: DiskSpace20%Free
        eval_time: 2m
      - alertname: DiskSpace20%Free
        eval_time: 3m
        exp_alerts:
          - exp_labels:
              severity: moderate
              instance: rfmfxevnt-vp1:9100
              mountpoint: /
          - exp_annotations:
             description: 'Diskspace on rfmfxevnt-vp1:9100 filesystem / has 19% available.'