From 49af37b7ab733135b3b1ad15cff568c0a88c2bd2 Mon Sep 17 00:00:00 2001
From: "Michael B. Gale" <mbg@github.com>
Date: Fri, 13 Mar 2026 13:25:15 +0000
Subject: [PATCH] Add tests for `release-branches.ts`

---
 pr-checks/release-branches.test.ts | 61 ++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 pr-checks/release-branches.test.ts

diff --git a/pr-checks/release-branches.test.ts b/pr-checks/release-branches.test.ts
new file mode 100644
index 000000000..b33c7b85a
--- /dev/null
+++ b/pr-checks/release-branches.test.ts
@@ -0,0 +1,61 @@
+#!/usr/bin/env npx tsx
+
+/*
+Tests for the release-branches.ts script
+*/
+
+import * as assert from "node:assert/strict";
+import { describe, it } from "node:test";
+
+import { computeBackportBranches } from "./release-branches";
+
+describe("computeBackportBranches", async () => {
+  await it("rejects invalid major versions", () => {
+    // The majorVersion is expected to be in vN format.
+    assert.throws(() => computeBackportBranches("3", "v4.28.0", 3));
+    assert.throws(() => computeBackportBranches("v3.1", "v4.28.0", 3));
+  });
+
+  await it("rejects invalid latest tags", () => {
+    // The latestTag is expected to be in vN.M.P format.
+    assert.throws(() => computeBackportBranches("v3", "v4", 3));
+    assert.throws(() => computeBackportBranches("v3", "4", 3));
+    assert.throws(() => computeBackportBranches("v3", "v4.28", 3));
+    assert.throws(() => computeBackportBranches("v3", "4.28", 3));
+    assert.throws(() => computeBackportBranches("v3", "4.28.0", 3));
+  });
+
+  await it("sets backport source branch based on major version", () => {
+    // Test that the backport source branch is releases/v{majorVersion}
+    const result = computeBackportBranches("v3", "v4.28.0", 3);
+    assert.equal(result.backportSourceBranch, "releases/v3");
+  });
+
+  await it("no backport targets when major version is the oldest supported", () => {
+    // When majorVersion equals the major version of latestTag and we do not support older major versions,
+    // then there are no older supported branches to backport to.
+    const result = computeBackportBranches("v3", "v3.28.0", 3);
+    assert.deepEqual(result.backportTargetBranches, []);
+  });
+
+  await it("backports to older supported major versions", () => {
+    const result = computeBackportBranches("v4", "v4.1.0", 3);
+    assert.equal(result.backportSourceBranch, "releases/v4");
+    assert.deepEqual(result.backportTargetBranches, ["releases/v3"]);
+  });
+
+  await it("backports to multiple older supported branches", () => {
+    const result = computeBackportBranches("v5", "v5.0.0", 3);
+    assert.equal(result.backportSourceBranch, "releases/v5");
+    assert.deepEqual(result.backportTargetBranches, [
+      "releases/v4",
+      "releases/v3",
+    ]);
+  });
+
+  await it("does not backport when major version is older than latest tag", () => {
+    const result = computeBackportBranches("v2", "v3.28.0", 2);
+    assert.equal(result.backportSourceBranch, "releases/v2");
+    assert.deepEqual(result.backportTargetBranches, []);
+  });
+});