diff --git a/src/commands/signal-install.test.ts b/src/commands/signal-install.test.ts
new file mode 100644
index 000000000..018caf6c9
--- /dev/null
+++ b/src/commands/signal-install.test.ts
@@ -0,0 +1,128 @@
+import { describe, expect, it } from "vitest";
+import type { ReleaseAsset } from "./signal-install.js";
+import { looksLikeArchive, pickAsset } from "./signal-install.js";
+
+// Realistic asset list modelled after an actual signal-cli GitHub release.
+const SAMPLE_ASSETS: ReleaseAsset[] = [
+  {
+    name: "signal-cli-0.13.14-Linux-native.tar.gz",
+    browser_download_url: "https://example.com/linux-native.tar.gz",
+  },
+  {
+    name: "signal-cli-0.13.14-Linux-native.tar.gz.asc",
+    browser_download_url: "https://example.com/linux-native.tar.gz.asc",
+  },
+  {
+    name: "signal-cli-0.13.14-macOS-native.tar.gz",
+    browser_download_url: "https://example.com/macos-native.tar.gz",
+  },
+  {
+    name: "signal-cli-0.13.14-macOS-native.tar.gz.asc",
+    browser_download_url: "https://example.com/macos-native.tar.gz.asc",
+  },
+  {
+    name: "signal-cli-0.13.14-Windows-native.zip",
+    browser_download_url: "https://example.com/windows-native.zip",
+  },
+  {
+    name: "signal-cli-0.13.14-Windows-native.zip.asc",
+    browser_download_url: "https://example.com/windows-native.zip.asc",
+  },
+  { name: "signal-cli-0.13.14.tar.gz", browser_download_url: "https://example.com/jvm.tar.gz" },
+  {
+    name: "signal-cli-0.13.14.tar.gz.asc",
+    browser_download_url: "https://example.com/jvm.tar.gz.asc",
+  },
+];
+
+describe("looksLikeArchive", () => {
+  it("recognises .tar.gz", () => {
+    expect(looksLikeArchive("foo.tar.gz")).toBe(true);
+  });
+
+  it("recognises .tgz", () => {
+    expect(looksLikeArchive("foo.tgz")).toBe(true);
+  });
+
+  it("recognises .zip", () => {
+    expect(looksLikeArchive("foo.zip")).toBe(true);
+  });
+
+  it("rejects signature files", () => {
+    expect(looksLikeArchive("foo.tar.gz.asc")).toBe(false);
+  });
+
+  it("rejects unrelated files", () => {
+    expect(looksLikeArchive("README.md")).toBe(false);
+  });
+});
+
+describe("pickAsset", () => {
+  describe("linux", () => {
+    it("selects the Linux-native asset on x64", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "linux", "x64");
+      expect(result).toBeDefined();
+      expect(result!.name).toContain("Linux-native");
+      expect(result!.name).toMatch(/\.tar\.gz$/);
+    });
+
+    it("returns undefined on arm64 (triggers brew fallback)", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "linux", "arm64");
+      expect(result).toBeUndefined();
+    });
+
+    it("returns undefined on arm (32-bit)", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "linux", "arm");
+      expect(result).toBeUndefined();
+    });
+  });
+
+  describe("darwin", () => {
+    it("selects the macOS-native asset", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "darwin", "arm64");
+      expect(result).toBeDefined();
+      expect(result!.name).toContain("macOS-native");
+    });
+
+    it("selects the macOS-native asset on x64", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "darwin", "x64");
+      expect(result).toBeDefined();
+      expect(result!.name).toContain("macOS-native");
+    });
+  });
+
+  describe("win32", () => {
+    it("selects the Windows-native asset", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "win32", "x64");
+      expect(result).toBeDefined();
+      expect(result!.name).toContain("Windows-native");
+      expect(result!.name).toMatch(/\.zip$/);
+    });
+  });
+
+  describe("edge cases", () => {
+    it("returns undefined for an empty asset list", () => {
+      expect(pickAsset([], "linux", "x64")).toBeUndefined();
+    });
+
+    it("skips assets with missing name or url", () => {
+      const partial: ReleaseAsset[] = [
+        { name: "signal-cli.tar.gz" },
+        { browser_download_url: "https://example.com/file.tar.gz" },
+      ];
+      expect(pickAsset(partial, "linux", "x64")).toBeUndefined();
+    });
+
+    it("falls back to first archive for unknown platform", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "freebsd" as NodeJS.Platform, "x64");
+      expect(result).toBeDefined();
+      expect(result!.name).toMatch(/\.tar\.gz$/);
+    });
+
+    it("never selects .asc signature files", () => {
+      const result = pickAsset(SAMPLE_ASSETS, "linux", "x64");
+      expect(result).toBeDefined();
+      expect(result!.name).not.toMatch(/\.asc$/);
+    });
+  });
+});
diff --git a/src/commands/signal-install.ts b/src/commands/signal-install.ts
index 1f168cd9f..4e68a8131 100644
--- a/src/commands/signal-install.ts
+++ b/src/commands/signal-install.ts
@@ -9,12 +9,12 @@ import { resolveBrewExecutable } from "../infra/brew.js";
 import { runCommandWithTimeout } from "../process/exec.js";
 import { CONFIG_DIR } from "../utils.js";
 
-type ReleaseAsset = {
+export type ReleaseAsset = {
   name?: string;
   browser_download_url?: string;
 };
 
-type NamedAsset = {
+export type NamedAsset = {
   name: string;
   browser_download_url: string;
 };
@@ -31,7 +31,8 @@ export type SignalInstallResult = {
   error?: string;
 };
 
-function looksLikeArchive(name: string): boolean {
+/** @internal Exported for testing. */
+export function looksLikeArchive(name: string): boolean {
   return name.endsWith(".tar.gz") || name.endsWith(".tgz") || name.endsWith(".zip");
 }
 
@@ -43,7 +44,8 @@ function looksLikeArchive(name: string): boolean {
  * returns `undefined` so the caller can fall back to a different install
  * strategy (e.g. Homebrew).
  */
-function pickAsset(
+/** @internal Exported for testing. */
+export function pickAsset(
   assets: ReleaseAsset[],
   platform: NodeJS.Platform,
   arch: string,