swarm-ui: keep the table filter popover inside the window

frontend/packages/swarm-ui/test/popover-position.test.mjs

@@ -0,0 +1,17 @@
+// Where a table's filter popover sits. Run by `npm test`, which Node runs
+// with its built-in test runner and type stripping, so the `.ts` module is
+// imported as it is.
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { clampLeft } from "../src/ui/table/popover-position.ts";
+
+test("a popover near the right edge is pulled back on screen", () => {
+  // 300 wide in a 1000 wide window: the right edge may reach 992.
+  assert.equal(clampLeft(900, 300, 1000), 692);
+  assert.equal(clampLeft(100, 300, 1000), 100);
+});
+
+test("a popover never goes past the left edge", () => {
+  assert.equal(clampLeft(5, 300, 1000), 8);
+  assert.equal(clampLeft(50, 2000, 1000), 8);
+});