diff --git a/tests/cli/agent-selection.test.ts b/tests/cli/agent-selection.test.ts
new file mode 100644
index 0000000..1eb9aab
--- /dev/null
+++ b/tests/cli/agent-selection.test.ts
@@ -0,0 +1,60 @@
+import { describe, expect, test } from "bun:test";
+
+import { parseAgentSelection } from "../../src/cli/agent-selection";
+import { CliUsageError } from "../../src/cli/errors";
+
+describe("parseAgentSelection", () => {
+  test("selects Codex by default", () => {
+    expect(parseAgentSelection(["Create", "a", "Workflow"])).toEqual({
+      agentName: "codex",
+      values: ["Create", "a", "Workflow"],
+    });
+  });
+
+  test("selects Claude from a separate option value", () => {
+    expect(parseAgentSelection(["--agent", "claude", "Create it"])).toEqual({
+      agentName: "claude",
+      values: ["Create it"],
+    });
+  });
+
+  test("selects Pi from an inline option value", () => {
+    expect(parseAgentSelection(["--agent=pi", "Create it"])).toEqual({
+      agentName: "pi",
+      values: ["Create it"],
+    });
+  });
+
+  test("rejects a missing option value", () => {
+    expect(() => parseAgentSelection(["--agent"])).toThrow(
+      new CliUsageError(
+        "Invalid --agent value: (missing). Expected codex, claude, or pi.",
+      ),
+    );
+  });
+
+  test("rejects an unknown Agent", () => {
+    expect(() => parseAgentSelection(["--agent", "unknown"])).toThrow(
+      new CliUsageError(
+        "Invalid --agent value: unknown. Expected codex, claude, or pi.",
+      ),
+    );
+  });
+
+  test("rejects duplicate Agent options", () => {
+    expect(() =>
+      parseAgentSelection(["--agent=pi", "--agent", "claude"]),
+    ).toThrow(
+      new CliUsageError("The --agent option may only be specified once."),
+    );
+  });
+
+  test("preserves the order of remaining values", () => {
+    expect(
+      parseAgentSelection(["first", "--agent", "claude", "second", "third"]),
+    ).toEqual({
+      agentName: "claude",
+      values: ["first", "second", "third"],
+    });
+  });
+});