diff --git a/l4d2web/tests/test_admin_users.py b/l4d2web/tests/test_admin_users.py
new file mode 100644
index 0000000..5294e9e
--- /dev/null
+++ b/l4d2web/tests/test_admin_users.py
@@ -0,0 +1,260 @@
+import pytest
+from sqlalchemy import select
+
+from l4d2web.app import create_app
+from l4d2web.auth import hash_password
+from l4d2web.db import init_db, session_scope
+from l4d2web.models import Blueprint, Job, Overlay, Server, User
+
+
+@pytest.fixture
+def admin_client(tmp_path, monkeypatch):
+    """Returns a logged-in admin client + the admin's user id.
+
+    Also creates a second admin so delete-of-the-last-admin is not the
+    default scenario; tests that need that condition can prune.
+    """
+    db_url = f"sqlite:///{tmp_path/'admin_users.db'}"
+    monkeypatch.setenv("DATABASE_URL", db_url)
+    app = create_app({"TESTING": True, "DATABASE_URL": db_url, "SECRET_KEY": "test"})
+    init_db()
+
+    with session_scope() as db:
+        admin = User(username="admin", password_digest=hash_password("secret"), admin=True)
+        second_admin = User(username="admin2", password_digest=hash_password("secret"), admin=True)
+        db.add_all([admin, second_admin])
+        db.flush()
+        admin_id = admin.id
+
+    client = app.test_client()
+    with client.session_transaction() as sess:
+        sess["user_id"] = admin_id
+        sess["csrf_token"] = "test-token"
+    return client, admin_id
+
+
+def _add_user(username: str, *, admin: bool = False, active: bool = True) -> int:
+    with session_scope() as db:
+        u = User(
+            username=username,
+            password_digest=hash_password("secret"),
+            admin=admin,
+            active=active,
+        )
+        db.add(u)
+        db.flush()
+        return u.id
+
+
+def _user_exists(user_id: int) -> bool:
+    with session_scope() as db:
+        return db.scalar(select(User).where(User.id == user_id)) is not None
+
+
+def _user_active(user_id: int) -> bool:
+    with session_scope() as db:
+        u = db.scalar(select(User).where(User.id == user_id))
+        assert u is not None
+        return u.active
+
+
+def _post(client, path: str):
+    return client.post(path, headers={"X-CSRF-Token": "test-token"})
+
+
+# ---------------- deactivate / activate ----------------
+
+
+def test_deactivate_flips_active_false(admin_client):
+    client, _ = admin_client
+    target = _add_user("bob")
+
+    response = _post(client, f"/admin/users/{target}/deactivate")
+
+    assert response.status_code == 302
+    assert response.headers["Location"].endswith("/admin/users")
+    assert _user_active(target) is False
+
+
+def test_activate_flips_active_true(admin_client):
+    client, _ = admin_client
+    target = _add_user("bob", active=False)
+
+    response = _post(client, f"/admin/users/{target}/activate")
+
+    assert response.status_code == 302
+    assert _user_active(target) is True
+
+
+def test_deactivate_self_refused(admin_client):
+    client, admin_id = admin_client
+
+    response = _post(client, f"/admin/users/{admin_id}/deactivate")
+
+    assert response.status_code == 409
+    assert _user_active(admin_id) is True
+
+
+def test_deactivate_unknown_user_404(admin_client):
+    client, _ = admin_client
+
+    response = _post(client, "/admin/users/99999/deactivate")
+
+    assert response.status_code == 404
+
+
+def test_deactivated_user_cannot_log_in(admin_client):
+    client, _ = admin_client
+    target = _add_user("bob")
+    _post(client, f"/admin/users/{target}/deactivate")
+
+    # Fresh client — different session, no admin login.
+    fresh = client.application.test_client()
+    response = fresh.post(
+        "/login",
+        data={"username": "bob", "password": "secret"},
+        headers={"X-CSRF-Token": "test-token"},
+    )
+
+    # Same response as wrong-password / unknown-user (no leak about active).
+    assert response.status_code == 401
+
+
+def test_deactivated_user_existing_session_invalidated(admin_client):
+    """An active session at the moment of deactivation stops working."""
+    client, _ = admin_client
+    target = _add_user("bob")
+
+    # Forge a session for bob.
+    bob_client = client.application.test_client()
+    with bob_client.session_transaction() as sess:
+        sess["user_id"] = target
+        sess["csrf_token"] = "test-token"
+
+    # Sanity: bob can hit a logged-in route.
+    pre = bob_client.get("/dashboard")
+    assert pre.status_code == 200
+
+    # Admin deactivates bob.
+    _post(client, f"/admin/users/{target}/deactivate")
+
+    # bob's session should now be treated as logged-out → /dashboard redirects to /login.
+    post = bob_client.get("/dashboard", follow_redirects=False)
+    assert post.status_code == 302
+    assert "/login" in post.headers["Location"]
+
+
+# ---------------- delete: refusal cases ----------------
+
+
+def test_delete_self_refused(admin_client):
+    client, admin_id = admin_client
+
+    response = _post(client, f"/admin/users/{admin_id}/delete")
+
+    assert response.status_code == 409
+    assert _user_exists(admin_id)
+
+
+def test_delete_other_admin_succeeds_when_more_than_one_admin(admin_client):
+    """The fixture creates 2 admins; admin can delete admin2."""
+    client, _ = admin_client
+    with session_scope() as db:
+        admin2 = db.scalar(select(User).where(User.username == "admin2"))
+        admin2_id = admin2.id
+
+    response = _post(client, f"/admin/users/{admin2_id}/delete")
+
+    assert response.status_code == 302
+    assert not _user_exists(admin2_id)
+
+
+# Note: the "last admin refused" branch in admin_users_delete is defense-
+# in-depth. Through normal flow it's unreachable: a non-admin can't reach
+# the endpoint (@require_admin), and an admin trying to delete the only
+# remaining admin must be deleting themselves — which the self-delete
+# check rejects first. The branch is kept anyway in case the auth model
+# ever evolves (e.g. service accounts that bypass require_admin).
+
+
+def test_delete_blocked_when_owns_servers(admin_client):
+    client, _ = admin_client
+    target = _add_user("bob")
+    with session_scope() as db:
+        bp = Blueprint(user_id=target, name="bp", arguments="[]", config="[]")
+        db.add(bp)
+        db.flush()
+        db.add(Server(user_id=target, blueprint_id=bp.id, name="alpha", port=27015))
+
+    response = _post(client, f"/admin/users/{target}/delete")
+
+    assert response.status_code == 409
+    assert b"server" in response.data
+    assert _user_exists(target)
+
+
+def test_delete_blocked_when_owns_blueprints(admin_client):
+    client, _ = admin_client
+    target = _add_user("bob")
+    with session_scope() as db:
+        db.add(Blueprint(user_id=target, name="bp", arguments="[]", config="[]"))
+
+    response = _post(client, f"/admin/users/{target}/delete")
+
+    assert response.status_code == 409
+    assert b"blueprint" in response.data
+    assert _user_exists(target)
+
+
+def test_delete_blocked_when_owns_custom_overlays(admin_client):
+    client, _ = admin_client
+    target = _add_user("bob")
+    with session_scope() as db:
+        db.add(Overlay(name="custom", path="/opt/custom", user_id=target))
+
+    response = _post(client, f"/admin/users/{target}/delete")
+
+    assert response.status_code == 409
+    assert b"overlay" in response.data
+    assert _user_exists(target)
+
+
+def test_delete_unknown_user_404(admin_client):
+    client, _ = admin_client
+
+    response = _post(client, "/admin/users/99999/delete")
+
+    assert response.status_code == 404
+
+
+# ---------------- delete: success cases ----------------
+
+
+def test_delete_succeeds_for_orphan(admin_client):
+    client, _ = admin_client
+    target = _add_user("bob")
+
+    response = _post(client, f"/admin/users/{target}/delete")
+
+    assert response.status_code == 302
+    assert response.headers["Location"].endswith("/admin/users")
+    assert not _user_exists(target)
+
+
+def test_delete_succeeds_when_user_only_owns_jobs(admin_client):
+    """Job rows have nullable user_id and are kept as audit trail."""
+    client, _ = admin_client
+    target = _add_user("bob")
+    with session_scope() as db:
+        db.add(Job(user_id=target, server_id=None, operation="install", state="done"))
+        db.flush()
+
+    response = _post(client, f"/admin/users/{target}/delete")
+
+    assert response.status_code == 302
+    assert not _user_exists(target)
+    # The Job row survives, but its user_id is now NULL.
+    with session_scope() as db:
+        jobs = db.scalars(select(Job)).all()
+        assert len(jobs) == 1
+        assert jobs[0].user_id is None