ref(crons): Add test file for timeline utils (#51101)

Simple test file for now, but with the new frontend bucketing on the
timeline view there will be more functions/tests here shortly

Fixes: https://github.com/getsentry/sentry/issues/51098

static/app/views/monitors/components/overviewTimeline/utils.spec.tsx

@@ -0,0 +1,35 @@
+import {getStartFromTimeWindow} from 'sentry/views/monitors/components/overviewTimeline/utils';
+
+describe('Crons Timeline Utils', function () {
+  const end = new Date('2023-06-15T12:00:00Z');
+
+  describe('getStartFromTimeWindow', function () {
+    it('correctly computes for 1h', function () {
+      const expectedStart = new Date('2023-06-15T11:00:00Z');
+      const start = getStartFromTimeWindow(end, '1h');
+
+      expect(start).toEqual(expectedStart);
+    });
+
+    it('correctly computes for 24h', function () {
+      const expectedStart = new Date('2023-06-14T12:00:00Z');
+      const start = getStartFromTimeWindow(end, '24h');
+
+      expect(start).toEqual(expectedStart);
+    });
+
+    it('correctly computes for 7d', function () {
+      const expectedStart = new Date('2023-06-08T12:00:00Z');
+      const start = getStartFromTimeWindow(end, '7d');
+
+      expect(start).toEqual(expectedStart);
+    });
+
+    it('correctly computes for 30d', function () {
+      const expectedStart = new Date('2023-05-16T12:00:00Z');
+      const start = getStartFromTimeWindow(end, '30d');
+
+      expect(start).toEqual(expectedStart);
+    });
+  });
+});