diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 59aaa6b..f9ec440 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -7,27 +7,25 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [2.7, 3.6, 3.7, 3.8, 3.9]
+        python-version:
+          ["3.8.*", "3.9.*", "3.10.*", "3.11.*", "3.12.*", "3.13.*"]
     steps:
-    - uses: actions/checkout@master
-    - name: set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
-      with:
-        python-version: ${{ matrix.python-version }}
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        pip install -U setuptools
-        pip install -r requirements.txt
-        pip install .
-    - name: Run mypy
-      if: "matrix.python-version != '2.7' && matrix.python-version != 'pypy2'"
-      run: |
+      - uses: actions/checkout@master
+      - name: set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -U setuptools
+          pip install -r requirements.txt
+          pip install .
+          pip install tox
+      - name: Run mypy
+        run: |
           pip install -U mypy
           mypy -p zxcvbn --ignore-missing-imports
-    - name: Run tests
-      run: |
-          pytest -v 
-    - name: Test Compatibility
-      run: |
-          python tests/test_compatibility.py tests/password_expected_value.json
+      - name: Run tests
+        run: |
+          tox
diff --git a/README.rst b/README.rst
index fb3d411..b41a3af 100644
--- a/README.rst
+++ b/README.rst
@@ -16,7 +16,7 @@ time.
 
 Features
 --------
-- **Tested in Python versions 2.7, 3.6-3.9**
+- **Tested in Python versions 3.8-3.13**
 - Accepts user data to be added to the dictionaries that are tested against (name, birthdate, etc)
 - Gives a score to the password, from 0 (terrible) to 4 (great)
 - Provides feedback on the password and ways to improve it
diff --git a/requirements.txt b/requirements.txt
index e0fa86f..5ac1407 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +1,5 @@
-pytest==3.5.0
+# For older Python versions < 3.6 install Pytest 3.5.0
+pytest==3.5.0; python_version < "3.6"
+
+# For Python 3.6+, install a more modern Pytest:
+pytest==7.4.2; python_version >= "3.6"
diff --git a/tests/zxcvbn_test.py b/tests/zxcvbn_test.py
index 6f1bda3..6dce19d 100644
--- a/tests/zxcvbn_test.py
+++ b/tests/zxcvbn_test.py
@@ -36,3 +36,12 @@ def test_dictionary_password():
     assert result["feedback"]["warning"] == \
            "A word by itself is easy to guess.", \
            "Gives specific error for single-word passwords"
+
+def test_empty_password():
+    input_ = None
+    password = ""
+
+    try:
+      zxcvbn(password, user_inputs=[input_])
+    except IndexError as ie:
+        assert False, "Empty password raised IndexError"
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..f73fe62
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,10 @@
+[tox]
+envlist = py38, py39, py310, py311, py312, py313
+isolated_build = True
+
+[testenv]
+deps =
+    pytest
+commands =
+    pytest
+    python tests/test_compatibility.py tests/password_expected_value.json
diff --git a/zxcvbn/scoring.py b/zxcvbn/scoring.py
index 49fa13d..4e3cbc0 100644
--- a/zxcvbn/scoring.py
+++ b/zxcvbn/scoring.py
@@ -173,6 +173,10 @@ def make_bruteforce_match(i, j):
     # helper: step backwards through optimal.m starting at the end,
     # constructing the final optimal match sequence.
     def unwind(n):
+        if n == 0:
+            # return empty list for zero-length password
+            return []
+
         optimal_match_sequence = []
         k = n - 1
         # find the final best sequence length and score