From a58fa4a2c59968df4fb2ce85da20fd062170a4f8 Mon Sep 17 00:00:00 2001
From: Richard Hansen <rhansen@rhansen.org>
Date: Mon, 12 Apr 2021 03:43:17 -0400
Subject: [PATCH] tests: Add tests for `SkipList.atOffset()`

---
 src/tests/frontend/specs/skiplist.js | 36 ++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/src/tests/frontend/specs/skiplist.js b/src/tests/frontend/specs/skiplist.js
index 4b2ebd5aa..16b985615 100644
--- a/src/tests/frontend/specs/skiplist.js
+++ b/src/tests/frontend/specs/skiplist.js
@@ -15,4 +15,40 @@ describe('skiplist.js', function () {
     skiplist.push({key: 'foo'});
     expect(() => skiplist.push({key: 'foo'})).to.throwError();
   });
+
+  it('atOffset() returns last entry that touches offset', async function () {
+    const skiplist = new SkipList();
+    const entries = [];
+    let nextId = 0;
+    const makeEntry = (width) => {
+      const entry = {key: `id${nextId++}`, width};
+      entries.push(entry);
+      return entry;
+    };
+
+    skiplist.push(makeEntry(5));
+    expect(skiplist.atOffset(4)).to.be(entries[0]);
+    expect(skiplist.atOffset(5)).to.be(entries[0]);
+    expect(() => skiplist.atOffset(6)).to.throwError();
+
+    skiplist.push(makeEntry(0));
+    expect(skiplist.atOffset(4)).to.be(entries[0]);
+    expect(skiplist.atOffset(5)).to.be(entries[1]);
+    expect(() => skiplist.atOffset(6)).to.throwError();
+
+    skiplist.push(makeEntry(0));
+    expect(skiplist.atOffset(4)).to.be(entries[0]);
+    expect(skiplist.atOffset(5)).to.be(entries[2]);
+    expect(() => skiplist.atOffset(6)).to.throwError();
+
+    skiplist.splice(2, 0, [makeEntry(0)]);
+    expect(skiplist.atOffset(4)).to.be(entries[0]);
+    expect(skiplist.atOffset(5)).to.be(entries[2]);
+    expect(() => skiplist.atOffset(6)).to.throwError();
+
+    skiplist.push(makeEntry(3));
+    expect(skiplist.atOffset(4)).to.be(entries[0]);
+    expect(skiplist.atOffset(5)).to.be(entries[4]);
+    expect(skiplist.atOffset(6)).to.be(entries[4]);
+  });
 });