diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
new file mode 100644
index 00000000..5555107e
--- /dev/null
+++ b/.github/workflows/testing.yml
@@ -0,0 +1,32 @@
+name: testing
+
+on:
+  pull_request:
+  push:
+    branches: [master]
+
+jobs:
+  testing:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+
+      - name: Install pytest-cov, codecov
+        run: |
+          pip install pytest-cov codecov
+
+      - name: Test with pytest
+        run: |          
+          python -m pytest --cov=./
+
+      - name: Upload to CodeCov
+        uses: codecov/codecov-action@v1
diff --git a/environment.yml b/environment.yml
index f81a135f..67687d42 100644
--- a/environment.yml
+++ b/environment.yml
@@ -18,6 +18,9 @@ dependencies:
   - email-validator
   - phonenumbers  # phonenumberslite?
 
+  # Testing
+  - pytest
+
   # Development (Tools, Style, Linting)
   - ipython
   - black
diff --git a/requirements.txt b/requirements.txt
index 93809011..803e6f89 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,6 +7,9 @@ pydantic
 email-validator
 phonenumbers
 
+# testing
+pytest
+
 # dev
 ipython
 black
diff --git a/tests/test_compass_core_errors.py b/tests/test_compass_core_errors.py
new file mode 100644
index 00000000..5961a4fa
--- /dev/null
+++ b/tests/test_compass_core_errors.py
@@ -0,0 +1,83 @@
+import pytest
+
+from compass.core import errors
+
+
+class TestErrors:
+    def test_compass_error(self):
+        # Given
+        data = "message"
+
+        # Then
+        with pytest.raises(errors.CompassError, match=data):
+            # When
+            raise errors.CompassError(data)
+
+    def test_compass_authentication_error(self):
+        # Given
+        data = "message"
+
+        # Then
+        with pytest.raises(errors.CompassAuthenticationError, match=data):
+            # When
+            raise errors.CompassAuthenticationError(data)
+
+    def test_compass_report_error(self):
+        # Given
+        data = "message"
+
+        # Then
+        with pytest.raises(errors.CompassReportError, match=data):
+            # When
+            raise errors.CompassReportError(data)
+
+    def test_compass_report_permission_error(self):
+        # Given
+        data = "message"
+
+        # Then
+        with pytest.raises(errors.CompassReportPermissionError, match=data):
+            # When
+            raise errors.CompassReportPermissionError(data)
+
+    def test_compass_authentication_error_inheritance(self):
+        # Given
+        data = "message"
+
+        # When
+        try:
+            raise errors.CompassAuthenticationError(data)
+        # Then
+        except errors.CompassError as err:
+            assert str(err) == data
+
+    def test_compass_report_error_inheritance(self):
+        # Given
+        data = "message"
+
+        # When
+        try:
+            raise errors.CompassReportError(data)
+        # Then
+        except errors.CompassError as err:
+            assert str(err) == data
+
+    def test_compass_report_permission_error_inheritance(self):
+        # Given
+        data = "message"
+
+        # Dual inheritance:
+
+        # When
+        try:
+            raise errors.CompassReportPermissionError(data)
+        # Then
+        except PermissionError as err:
+            assert str(err) == data
+
+        # When
+        try:
+            raise errors.CompassReportPermissionError(data)
+        # Then
+        except errors.CompassError as err:
+            assert str(err) == data
diff --git a/tests/test_compass_core_interface_base.py b/tests/test_compass_core_interface_base.py
new file mode 100644
index 00000000..274f078f
--- /dev/null
+++ b/tests/test_compass_core_interface_base.py
@@ -0,0 +1,62 @@
+from pytest import MonkeyPatch
+import requests
+
+from compass.core.interface_base import InterfaceBase
+from compass.core.settings import Settings
+
+
+class TestInterfaceBase:
+    def test_get(self, monkeypatch: MonkeyPatch):
+        # Given
+        data = "https://example.org"
+        reqs = Settings.total_requests
+
+        # When
+        s = requests.Session()
+        monkeypatch.setattr(s, "get", lambda *args, **kwargs: dict(args=args, kwargs=kwargs))
+        result = InterfaceBase(s)._get(data)  # pylint: disable=protected-access
+
+        # Then
+        assert result["args"][0] == data
+        assert reqs + 1 == Settings.total_requests
+
+    def test_post(self, monkeypatch: MonkeyPatch):
+        # Given
+        data = "https://example.org"
+        json = {"abc": 123, "xyz": 321}
+        reqs = Settings.total_requests
+
+        # When
+        s = requests.Session()
+        monkeypatch.setattr(s, "post", lambda *args, **kwargs: dict(args=args, kwargs=kwargs))
+        result = InterfaceBase(s)._post(data, json=json)  # pylint: disable=protected-access
+
+        # Then
+        assert result["args"][0] == data
+        assert result["kwargs"]["json"] == json
+        assert reqs + 1 == Settings.total_requests
+
+    def test_head(self, monkeypatch: MonkeyPatch):
+        # Given
+        data = "https://example.org"
+        reqs = Settings.total_requests
+
+        # When
+        s = requests.Session()
+        monkeypatch.setattr(s, "head", lambda *args, **kwargs: dict(args=args, kwargs=kwargs))
+        result = InterfaceBase(s)._head(data)  # pylint: disable=protected-access
+
+        # Then
+        assert result["args"][0] == data
+        assert reqs + 1 == Settings.total_requests
+
+    def test_update_headers(self):
+        # Given
+        data = {"header_one": 123, "abc_xyz": 321}
+
+        # When
+        ib = InterfaceBase(requests.Session())
+        ib._update_headers(data)  # pylint: disable=protected-access
+
+        # Then
+        assert data.items() <= ib.s.headers.items()
diff --git a/tests/test_compass_core_settings.py b/tests/test_compass_core_settings.py
new file mode 100644
index 00000000..6fd60cbf
--- /dev/null
+++ b/tests/test_compass_core_settings.py
@@ -0,0 +1,56 @@
+from urllib.parse import urlparse
+
+import _strptime
+
+from compass.core.settings import Settings
+
+
+class TestSettings:
+    def test_base_url(self):
+        # Given
+        data = Settings.base_url
+
+        # When
+        result = urlparse(data)
+
+        # Then
+        assert isinstance(data, str)
+        assert bool(result.scheme) and bool(result.hostname)
+
+    def test_date_format(self):
+        # Given
+        data = Settings.date_format
+
+        # When
+        result = _strptime._TimeRE_cache.pattern(data)  # pylint: disable=protected-access
+
+        # Then
+        assert isinstance(data, str)
+        assert bool(result)
+
+    def test_org_number(self):
+        # Given When
+        data = Settings.org_number
+
+        # Then
+        assert isinstance(data, int)
+        assert 0 < data < 100_000_000  # IDs are between 1 and 99,999,999
+
+    def test_wcf_json_endpoint(self):
+        # Given When
+        data = Settings.wcf_json_endpoint
+
+        assert isinstance(data, str)
+        assert data[0] == "/"
+        assert ".svc" in data
+
+    def test_web_service_path(self):
+        # Given
+        data = Settings.web_service_path
+
+        # When
+        result = urlparse(data)
+
+        # Then
+        assert isinstance(data, str)
+        assert bool(result.scheme) and bool(result.hostname) and bool(result.path)
diff --git a/tests/test_compass_core_utility.py b/tests/test_compass_core_utility.py
new file mode 100644
index 00000000..bd67ba11
--- /dev/null
+++ b/tests/test_compass_core_utility.py
@@ -0,0 +1,165 @@
+import datetime
+
+import pytest
+
+from compass.core import utility
+
+
+class TestUtility:
+    def test_hash_code(self):
+        # Given
+        data = "testing"
+
+        # When
+        result = utility.hash_code(data)
+
+        # Then
+        assert isinstance(result, int)
+        # TODO Aim for property based aspects instead of fixed values!
+        assert result == -1422446064  # TODO max/min = +/- 2**32?
+
+    def test_compass_restify(self):
+        # Given
+        data = {"a": 1, "b": 2, "c": 3}
+        num_pairs = len(data)
+
+        # When
+        result = utility.compass_restify(data)
+
+        # Then
+        assert isinstance(result, list)
+        assert len(result) == num_pairs
+        assert all(item.keys() == {"Key", "Value"} for item in result)
+        # TODO Aim for property based aspects instead of fixed values!
+        assert result == [{"Key": "a", "Value": "1"}, {"Key": "b", "Value": "2"}, {"Key": "c", "Value": "3"}]
+
+    def test_cast_ast_eval_false_int(self):
+        # Given
+        data = 123
+
+        # When
+        result = utility.cast(data, ast_eval=False)
+        result_str = utility.cast(str(data), ast_eval=False)
+
+        # Then
+        assert result == data
+        assert result_str == data
+
+    def test_cast_ast_eval_false_str(self):
+        # Given
+        data = "abc"
+
+        # When
+        result = utility.cast(data, ast_eval=False)
+
+        # Then
+        assert result == data
+
+    def test_cast_ast_eval_false_list(self):
+        # Given
+        data = [1, 2, 3]
+
+        # When
+        result = utility.cast(data, ast_eval=False)
+        result_str = utility.cast(str(data), ast_eval=False)
+
+        # Then
+        assert result == str(data)
+        assert result_str == str(data)
+
+    def test_cast_ast_eval_true_int(self):
+        # Given
+        data = 123
+
+        # When
+        result = utility.cast(data, ast_eval=True)
+        result_str = utility.cast(str(data), ast_eval=True)
+
+        # Then
+        assert result == data
+        assert result_str == data
+
+    def test_cast_ast_eval_true_str(self):
+        # Given
+        data = "abc"
+
+        # When
+        result = utility.cast(data, ast_eval=True)
+
+        # Then
+        assert result == data
+
+    def test_cast_ast_eval_true_list(self):
+        # Given
+        data = [1, 2, 3]
+
+        # When
+        result = utility.cast(data, ast_eval=True)
+        result_str = utility.cast(str(data), ast_eval=True)
+
+        # Then
+        assert result == data
+        assert result_str == data
+
+    def test_maybe_int_int(self):
+        # Given
+        data = 123
+
+        # When
+        result = utility.maybe_int(data)
+        result_str = utility.cast(str(data))
+
+        # Then
+        assert result == data
+        assert result_str == data
+
+    def test_maybe_int_str(self):
+        # Given
+        data = "abc"
+
+        # When
+        result = utility.maybe_int(data)
+
+        # Then
+        assert result is None
+
+    def test_parse_month_short(self):
+        # Given
+        data = "01 Jan 2000"
+
+        # When
+        result = utility.parse(data)
+
+        # Then
+        assert isinstance(result, datetime.datetime)
+        assert result == datetime.datetime(2000, 1, 1)
+
+    def test_parse_month_long(self):
+        # Given
+        data = "01 January 2000"
+
+        # When
+        result = utility.parse(data)
+
+        # Then
+        assert isinstance(result, datetime.datetime)
+        assert result == datetime.datetime(2000, 1, 1)
+
+    def test_parse_non_date(self):
+        # Given
+        data = "abc"
+
+        # Then
+        with pytest.raises(ValueError):
+            # When
+            utility.parse(data)
+
+    def test_parse_empty(self):
+        # Given
+        data = ""
+
+        # When
+        result = utility.parse(data)
+
+        # Then
+        assert result is None