Add shell plugin model tests

test/shell.d/monitor-test.sh

@@ -0,0 +1,39 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
+
+run_node_test <<'JS'
+const monitor = requireFromRoot('shell/plugins/monitor/MonitorModel.js')
+
+assertEqual(monitor.clampBrightness(0), 1, 'monitor clamps minimum brightness')
+assertEqual(monitor.clampBrightness(101), 100, 'monitor clamps maximum brightness')
+assertEqual(monitor.clampBrightness(42.4), 42, 'monitor rounds brightness')
+assertEqual(monitor.clampBrightness('nope'), 1, 'monitor rejects invalid brightness')
+
+assertEqual(monitor.normalizeScale('1.250'), '1.25', 'monitor normalizes fractional scale')
+assertEqual(monitor.normalizeScale('nope'), '', 'monitor rejects invalid scale')
+
+assertEqual(monitor.brightnessName(96), 'Sun blast', 'monitor names very bright displays')
+assertEqual(monitor.brightnessName(12), 'Candlelit', 'monitor names dim displays')
+
+assertDeepEqual(
+  monitor.parseDisplays(JSON.stringify([
+    { name: 'eDP-1', enabled: true },
+    { name: 'HDMI-A-1', enabled: false },
+    { name: 'DP-1', enabled: true }
+  ])),
+  {
+    displays: [
+      { name: 'eDP-1', enabled: true },
+      { name: 'HDMI-A-1', enabled: false },
+      { name: 'DP-1', enabled: true }
+    ],
+    enabledDisplayCount: 2
+  },
+  'monitor parses display state'
+)
+
+assertDeepEqual(monitor.parseDisplays('{'), { displays: [], enabledDisplayCount: 0 }, 'monitor handles invalid display JSON')
+JS