diff --git a/actions/setup/js/check_runs_helpers.test.cjs b/actions/setup/js/check_runs_helpers.test.cjs
new file mode 100644
index 00000000000..325f7111312
--- /dev/null
+++ b/actions/setup/js/check_runs_helpers.test.cjs
@@ -0,0 +1,125 @@
+// @ts-check
+import { describe, it, expect } from "vitest";
+import { createRequire } from "module";
+
+const req = createRequire(import.meta.url);
+const { isDeploymentCheck, selectLatestRelevantChecks, getFailingChecks } = req("./check_runs_helpers.cjs");
+
+describe("check_runs_helpers", () => {
+  describe("isDeploymentCheck", () => {
+    it("returns true when app slug is github-deployments", () => {
+      expect(isDeploymentCheck({ app: { slug: "github-deployments" } })).toBe(true);
+    });
+
+    it("returns false for non-deployment check runs", () => {
+      expect(isDeploymentCheck({ app: { slug: "github-actions" } })).toBe(false);
+    });
+
+    it("returns false when app is absent", () => {
+      expect(isDeploymentCheck({ name: "CI" })).toBe(false);
+    });
+
+    it("returns false for null/undefined", () => {
+      expect(isDeploymentCheck(null)).toBe(false);
+      expect(isDeploymentCheck(undefined)).toBe(false);
+    });
+  });
+
+  describe("selectLatestRelevantChecks", () => {
+    /** @type {any[]} */
+    const runs = [
+      { id: 1, name: "CI", status: "completed", conclusion: "success", started_at: "2024-01-01T00:00:00Z", app: { slug: "github-actions" } },
+      { id: 2, name: "CI", status: "completed", conclusion: "failure", started_at: "2024-01-02T00:00:00Z", app: { slug: "github-actions" } },
+      { id: 3, name: "Lint", status: "completed", conclusion: "success", started_at: "2024-01-01T00:00:00Z", app: { slug: "github-actions" } },
+      { id: 4, name: "Deploy", status: "completed", conclusion: "success", started_at: "2024-01-01T00:00:00Z", app: { slug: "github-deployments" } },
+    ];
+
+    it("returns the latest run per name", () => {
+      const { relevant } = selectLatestRelevantChecks(runs);
+      const ci = relevant.find(r => r.name === "CI");
+      expect(ci?.id).toBe(2);
+    });
+
+    it("excludes deployment checks and reports count", () => {
+      const { relevant, deploymentCheckCount } = selectLatestRelevantChecks(runs);
+      expect(relevant.every(r => r.app?.slug !== "github-deployments")).toBe(true);
+      expect(deploymentCheckCount).toBe(1);
+    });
+
+    it("excludes runs in excludedCheckRunIds", () => {
+      const { relevant, currentRunFilterCount } = selectLatestRelevantChecks(runs, {
+        excludedCheckRunIds: new Set([2]),
+      });
+      expect(relevant.find(r => r.id === 2)).toBeUndefined();
+      expect(currentRunFilterCount).toBe(1);
+    });
+
+    it("filters by includeList", () => {
+      const { relevant } = selectLatestRelevantChecks(runs, { includeList: ["Lint"] });
+      expect(relevant.length).toBe(1);
+      expect(relevant[0].name).toBe("Lint");
+    });
+
+    it("filters by excludeList", () => {
+      const { relevant } = selectLatestRelevantChecks(runs, { excludeList: ["Lint"] });
+      expect(relevant.find(r => r.name === "Lint")).toBeUndefined();
+    });
+
+    it("returns empty array for empty input", () => {
+      const { relevant, deploymentCheckCount, currentRunFilterCount } = selectLatestRelevantChecks([]);
+      expect(relevant).toEqual([]);
+      expect(deploymentCheckCount).toBe(0);
+      expect(currentRunFilterCount).toBe(0);
+    });
+
+    it("ignores empty includeList (includes everything)", () => {
+      const { relevant } = selectLatestRelevantChecks(runs, { includeList: [] });
+      expect(relevant.length).toBe(2); // CI (latest) + Lint
+    });
+  });
+
+  describe("getFailingChecks", () => {
+    /** @type {any[]} */
+    const runs = [
+      { id: 1, status: "completed", conclusion: "success" },
+      { id: 2, status: "completed", conclusion: "failure" },
+      { id: 3, status: "completed", conclusion: "cancelled" },
+      { id: 4, status: "completed", conclusion: "timed_out" },
+      { id: 5, status: "in_progress", conclusion: null },
+      { id: 6, status: "completed", conclusion: null },
+    ];
+
+    it("includes failure, cancelled, and timed_out conclusions", () => {
+      const failing = getFailingChecks(runs);
+      const ids = failing.map(r => r.id);
+      expect(ids).toContain(2);
+      expect(ids).toContain(3);
+      expect(ids).toContain(4);
+    });
+
+    it("excludes success conclusion", () => {
+      const failing = getFailingChecks(runs);
+      expect(failing.find(r => r.id === 1)).toBeUndefined();
+    });
+
+    it("includes pending runs when allowPending is false (default)", () => {
+      const failing = getFailingChecks(runs);
+      expect(failing.find(r => r.id === 5)).toBeDefined();
+    });
+
+    it("excludes pending runs when allowPending is true", () => {
+      const failing = getFailingChecks(runs, { allowPending: true });
+      expect(failing.find(r => r.id === 5)).toBeUndefined();
+    });
+
+    it("excludes completed run with null conclusion", () => {
+      const failing = getFailingChecks(runs);
+      expect(failing.find(r => r.id === 6)).toBeUndefined();
+    });
+
+    it("returns empty array when no checks fail", () => {
+      const passing = [{ id: 1, status: "completed", conclusion: "success" }];
+      expect(getFailingChecks(passing)).toEqual([]);
+    });
+  });
+});