1 files changed, 31 insertions, 0 deletions
diff --git a/src/features/tabs/tab-groups.test.ts b/src/features/tabs/tab-groups.test.ts
index 83f273c..a09dbc8 100644
--- a/src/features/tabs/tab-groups.test.ts
+++ b/src/features/tabs/tab-groups.test.ts
@@ -6,6 +6,7 @@ import {
   groupDescendants,
   groupGutterPx,
   groupParentCandidates,
+  groupTone,
   lastRowIsGroup,
   visibleGroupParents,
 } from "./tab-groups";
@@ -103,6 +104,36 @@ describe("groupDescendants / directGroupChildren / groupParentCandidates", () =>
   });
 });
 
+describe("groupTone", () => {
+  it("rotates three colours by level, starting at the outermost box", () => {
+    expect([1, 2, 3, 4, 5, 6, 7].map(groupTone)).toEqual([
+      "secondary",
+      "success",
+      "accent",
+      "secondary",
+      "success",
+      "accent",
+      "secondary",
+    ]);
+  });
+
+  it("never gives a box the colour of its parent or grandparent", () => {
+    for (let level = 3; level <= 20; level++) {
+      expect(groupTone(level)).not.toBe(groupTone(level - 1));
+      expect(groupTone(level)).not.toBe(groupTone(level - 2));
+    }
+  });
+
+  it("never uses primary (reserved for the active tab)", () => {
+    for (let level = 1; level <= 6; level++) expect(groupTone(level)).not.toBe("primary");
+  });
+
+  it("stays in range for out-of-range levels", () => {
+    expect(groupTone(0)).toBe("accent");
+    expect(groupTone(-1)).toBe("success");
+  });
+});
+
 describe("groupBleedPx / groupGutterPx", () => {
   it("is zero without groups", () => {
     expect(groupGutterPx(0)).toBe(0);