diff --git a/.github/workflows/build-and-test.yaml b/.github/workflows/build-and-test.yaml
index e88a379..66ca0a7 100644
--- a/.github/workflows/build-and-test.yaml
+++ b/.github/workflows/build-and-test.yaml
@@ -12,20 +12,21 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     strategy:
       max-parallel: 4
       matrix:
         python-version:
-          - 2.7
-          - 3.6
-          - 3.7
-          - 3.8
-          - 3.9
+          - "3.7"
+          - "3.8"
+          - "3.9"
+          - "3.10"
+          - "3.11"
+          - "3.12"
+          - "3.13"
     steps:
     - uses: actions/checkout@v1
     - name: Set up Python ${{ matrix.python-version }}
-      if: matrix.python-version != '2.7'
       uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
@@ -35,12 +36,6 @@ jobs:
         pip install --upgrade pip
         pip install tox tox-gh-actions
 
-    - name: Test with tox ${{env.TOXENV}}
-      if: matrix.python-version == '3.6'
-      env:
-        TOXENV: py27,py36,coverage
-      run: tox
-
     - name: Test with tox Python 3.7
       if: matrix.python-version == '3.7'
       env:
@@ -59,8 +54,32 @@ jobs:
         TOXENV: py39
       run: tox
 
-    - name: Lint Test with tox Python 3.6
-      if: matrix.python-version == '3.6'
+    - name: Test with tox Python 3.10
+      if: matrix.python-version == '3.10'
+      env:
+        TOXENV: py310
+      run: tox
+
+    - name: Test with tox Python 3.11
+      if: matrix.python-version == '3.11'
+      env:
+        TOXENV: py311
+      run: tox
+
+    - name: Test with tox Python 3.12
+      if: matrix.python-version == '3.12'
+      env:
+        TOXENV: py312
+      run: tox
+
+    - name: Test with tox Python 3.13
+      if: matrix.python-version == '3.13'
+      env:
+        TOXENV: py313
+      run: tox
+
+    - name: Lint Test with tox Python 3.11
+      if: matrix.python-version == '3.11'
       env:
         TOXENV: lint
       run: tox
diff --git a/setup.py b/setup.py
index 2dbf983..2cadf4a 100644
--- a/setup.py
+++ b/setup.py
@@ -27,6 +27,7 @@ def get_long_desc():
 
 tests_requires = [
     'mock',
+    'requests-mock',
     'pytest',
     'pytest-cov',
 ]
diff --git a/src/pycrunch/cubes.py b/src/pycrunch/cubes.py
index cf3cb0e..972c916 100644
--- a/src/pycrunch/cubes.py
+++ b/src/pycrunch/cubes.py
@@ -74,8 +74,27 @@ def __init__(self, dataset):
         if not hasattr(dataset, "catalogs"):
             dataset.refresh()
         self._dataset = dataset
-        self._variables_by_alias = dataset.variables.by('alias')
-        self._variables_by_name = dataset.variables.by('name')
+        self._variables_cache = None
+        self._variables_by_alias_cache = None
+        self._variables_by_name_cache = None
+
+    @property
+    def _variables(self):
+        if self._variables_cache is None:
+            self._variables_cache = self._dataset.variables
+        return self._variables_cache
+
+    @property
+    def _variables_by_alias(self):
+        if self._variables_by_alias_cache is None:
+            self._variables_by_alias_cache = self._variables.by("alias")
+        return self._variables_by_alias_cache
+
+    @property
+    def _variables_by_name(self):
+        if self._variables_by_name_cache is None:
+            self._variables_by_name_cache = self._variables.by("name")
+        return self._variables_by_name_cache
 
     def prepare_dimensions(self, dimensions):
         """Return list of crunch expressions for each cube dimension.
@@ -107,17 +126,16 @@ def get_dimension_by_string(self, dim_str):
 
         :param dim_str: String representing URL, Name, or Alias of a variable
         """
-
-        if dim_str in self._dataset.variables.index:
+        if dim_str in self._variables.index:
             # When URL is provided, fetch variable from index
-            return self._dataset.variables.index[dim_str]
+            return self._variables.index[dim_str]
         elif dim_str in self._variables_by_alias:
             return self._variables_by_alias[dim_str]
         elif dim_str in self._variables_by_name:
             return self._variables_by_name[dim_str]
         elif 'subvariables/' in dim_str:
             var_url = dim_str.split('subvariables/')[0]
-            variable = self._dataset.variables.index[var_url]
+            variable = self._variables.index[var_url]
             return variable.entity.subvariables.index[dim_str]
 
         raise ValueError("Can't find variable {} in dataset {}".format(
diff --git a/tests/test_cube.py b/tests/test_cube.py
index 86e0ab0..a879669 100644
--- a/tests/test_cube.py
+++ b/tests/test_cube.py
@@ -42,8 +42,8 @@ def dimension_string_fixture(request):
     dim_str, str_type, dim, subvar = request.param
     preparer = DimensionsPreparer(Mock())
     preparer._dataset.variables.index = dict()
-    preparer._variables_by_alias = dict()
-    preparer._variables_by_name = dict()
+    preparer._variables_by_alias_cache = dict()
+    preparer._variables_by_name_cache = dict()
     if str_type == 'URL':
         preparer._dataset.variables.index[dim_str] = dim
     elif str_type == 'URL_SUBVAR':
diff --git a/tests/test_elements.py b/tests/test_elements.py
index b67da82..7717b8e 100644
--- a/tests/test_elements.py
+++ b/tests/test_elements.py
@@ -3,6 +3,7 @@
 from unittest import TestCase
 
 import requests
+import six
 
 from pycrunch import elements, shoji
 
@@ -38,7 +39,7 @@ def test_attribute_access(self):
     def test_attribute_error(self):
         foo = self.Foo(bar=42)
         msg = 'Foo has no attribute nope'
-        self.assertRaisesRegexp(AttributeError, msg, getattr, foo, 'nope')
+        six.assertRaisesRegex(self, AttributeError, msg, getattr, foo, 'nope')
 
     def test_copy(self):
         foo = self.Foo(bar=42)
@@ -165,7 +166,7 @@ def test_follow_uri_template(self):
     def test_follow_no_link(self):
         person = self.Person(session=None, self='some uri')
         msg = 'Person has no link foo'
-        self.assertRaisesRegexp(AttributeError, msg, person.follow, 'foo')
+        six.assertRaisesRegex(self, AttributeError, msg, person.follow, 'foo')
 
     def test_refresh(self):
         before = {
@@ -199,7 +200,7 @@ def test_refresh_no_response(self):
 
         person = self.Person(session=session_mock, self='some uri')
         msg = 'Response could not be parsed.'
-        self.assertRaisesRegexp(TypeError, msg, person.refresh)
+        six.assertRaisesRegex(self, TypeError, msg, person.refresh)
         session_mock.get.assert_called_once_with('some uri')
 
     def test_post(self):
diff --git a/tests/test_http.py b/tests/test_http.py
index b31fff1..f1a7235 100644
--- a/tests/test_http.py
+++ b/tests/test_http.py
@@ -2,6 +2,7 @@
 
 import pytest
 import requests
+import requests_mock
 
 from pycrunch import connect, connect_with_token, Session, __version__
 from pycrunch.lemonpy import ServerError
@@ -18,25 +19,23 @@
 
 class TestHTTPRequests(TestCase):
 
-    @classmethod
-    def setUpClass(cls):
-        cls.s = Session("not an email", "not a password", site_url="https://app.crunch.io/api/")
-        cls.r = cls.s.get("http://httpbin.org/headers")
+    def setUp(self):
+        self.s = Session("not an email", "not a password", site_url="https://app.crunch.io/api/")
+        adapter = requests_mock.Adapter()
+        adapter.register_uri('GET', "http://httpbin.org/headers", text='data')
+        self.s.mount("mock://", adapter)
 
     def test_request_sends_user_agent(self):
         pycrunch_ua = 'pycrunch/%s' % __version__
-        req_headers_sent = self.r.request.headers
-        req_headers_received = self.r.json()['headers']
-        self.assertTrue('user-agent' in req_headers_sent)
-        self.assertTrue('User-Agent' in req_headers_received)
-        self.assertTrue(pycrunch_ua in req_headers_sent.get('user-agent', ''))
-        self.assertTrue(pycrunch_ua in req_headers_received.get('User-Agent', ''))
+        resp = self.s.get('http://httpbin.org/headers')
+        req_headers_sent = resp.request.headers
+        assert 'user-agent' in req_headers_sent
+        assert pycrunch_ua in req_headers_sent.get('user-agent', '')
 
     def test_request_sends_gzip(self):
-        req_headers_sent = self.r.request.headers
-        req_headers_received = self.r.json()['headers']
+        resp = self.s.get('http://httpbin.org/headers')
+        req_headers_sent = resp.request.headers
         self.assertIn("gzip", req_headers_sent['Accept-Encoding'])
-        self.assertIn("gzip", req_headers_received['Accept-Encoding'])
 
 
 class TestHTTPResponses(TestCase):
diff --git a/tox.ini b/tox.ini
index f824e4b..66d3f80 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py27,py34,py35,py36,py37,py38,py39
+    py27,py34,py35,py36,py37,py38,py39,py310,py311,py312,py313
     coverage,lint
 
 [gh-actions]
@@ -8,7 +8,14 @@ python =
     2.7: py27
     3.4: py34
     3.5: py35
-    3.6: py27, py36, coverage, lint
+    3.6: py36
+    3.7: py37
+    3.8: py38
+    3.9: py39
+    3.10: py310
+    3.11: py311, coverage, lint
+    3.12: py312
+    3.13: py313
 
 [testenv]
 basepython =
@@ -19,8 +26,12 @@ basepython =
     py37: python3.7
     py38: python3.8
     py39: python3.9
+    py310: python3.10
+    py311: python3.11
+    py312: python3.12
+    py313: python3.13
     py2: python2.7
-    py3: python3.6
+    py3: python3.11
 
 commands =
     pip install pycrunch[testing]
@@ -31,7 +42,7 @@ setenv =
 
 [testenv:coverage]
 skip_install = True
-basepython = python3.6
+basepython = python3.11
 commands =
     coverage combine
     coverage report
@@ -42,7 +53,7 @@ setenv =
 
 [testenv:lint]
 skip_install = True
-basepython = python3.6
+basepython = python3.11
 commands =
     python setup.py check -r -s -m
     check-manifest