diff --git a/.github/workflows/linting.yml b/.github/workflows/linting.yml
index 0f8b521..5e88599 100644
--- a/.github/workflows/linting.yml
+++ b/.github/workflows/linting.yml
@@ -26,4 +26,4 @@ jobs:
       - name: flake8
         run: flake8 .
       - name: mypy
-        run: mypy .
+        run: mypy src && mypy tests
diff --git a/pyproject.toml b/pyproject.toml
index a5269ff..88890a6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -31,6 +31,8 @@ exclude = '^venv*|^.venv*|.git|.eggs|build|dist|.cache|.pytest_cache|.mypy_cache
 python_version = '3.11'
 warn_return_any = true
 warn_unused_configs = true
+# Let mypy find modules inside the 'src' directory when importing 'hd_active'.
+mypy_path = 'src'
 # Disable the warning below, from type hinting variables in a function.
 # By default, the bodies of untyped functions are not checked, consider using --check-untyped-defs
 disable_error_code = 'annotation-unchecked'
diff --git a/setup.cfg b/setup.cfg
index 090f019..014c1d4 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,7 +1,7 @@
 # Configuration for tools that don't support `pyproject.toml`.
 
 [flake8]
-exclude = .git,.github,.venv*,venv*,__pycache__,assets,src/hd_active/ui/forms,docs,site
+exclude = .git,.github,.venv*,venv*,__pycache__,assets,src/hd_active/ui/forms,docs,site,build
 max-line-length = 100
 
 # Errors being ignored:
diff --git a/src/hd_active/hd_active.py b/src/hd_active/hd_active.py
index b85cf63..7767c33 100644
--- a/src/hd_active/hd_active.py
+++ b/src/hd_active/hd_active.py
@@ -7,7 +7,7 @@
 from pathlib import Path
 from typing import Deque, Iterable, Optional, Set, Union
 
-from src.hd_active.hd_action_state import HdActionState
+from .hd_action_state import HdActionState
 
 FILE_NAME = '_hd_active.txt'
 logger = logging.getLogger(__name__)
@@ -148,7 +148,7 @@ def change_state(self) -> HdActionState:
     import argparse
     import sys
 
-    from src.hd_active.hd_active_config import HdActiveConfig
+    from .hd_active_config import HdActiveConfig
 
     parser = argparse.ArgumentParser(description='Keep HDs active.')
     parser.add_argument(
diff --git a/src/hd_active/main.py b/src/hd_active/main.py
index 3292aba..963f932 100644
--- a/src/hd_active/main.py
+++ b/src/hd_active/main.py
@@ -2,8 +2,8 @@
 
 from PySide6 import QtGui, QtWidgets
 
-from src.hd_active.ui.system_tray_icon import SystemTrayIcon
-from src.hd_active.utils import get_asset
+from .ui.system_tray_icon import SystemTrayIcon
+from .utils import get_asset
 
 
 def main():
diff --git a/src/hd_active/ui/log_dialog.py b/src/hd_active/ui/log_dialog.py
index 3b7a1c8..3a1f4a0 100644
--- a/src/hd_active/ui/log_dialog.py
+++ b/src/hd_active/ui/log_dialog.py
@@ -1,8 +1,8 @@
 from PySide6.QtGui import QShowEvent
 from PySide6.QtWidgets import QDialog, QWidget
 
-from src.hd_active.hd_active import HdActive
-from src.hd_active.ui.forms.ui_log_dialog import Ui_LogDialog
+from ..hd_active import HdActive
+from .forms.ui_log_dialog import Ui_LogDialog
 
 
 class LogDialog(QDialog, Ui_LogDialog):
diff --git a/src/hd_active/ui/settings_dialog.py b/src/hd_active/ui/settings_dialog.py
index e394f14..a2fffaa 100644
--- a/src/hd_active/ui/settings_dialog.py
+++ b/src/hd_active/ui/settings_dialog.py
@@ -1,8 +1,8 @@
 from PySide6.QtWidgets import QDialog, QWidget
 
-from src.hd_active.hd_active import HdActive
-from src.hd_active.ui.forms.ui_settings_dialog import Ui_SettingsDialog
-from src.hd_active.ui.log_dialog import LogDialog
+from ..hd_active import HdActive
+from .forms.ui_settings_dialog import Ui_SettingsDialog
+from .log_dialog import LogDialog
 
 
 class SettingsDialog(QDialog, Ui_SettingsDialog):
diff --git a/src/hd_active/ui/system_tray_icon.py b/src/hd_active/ui/system_tray_icon.py
index 6b156a8..40d6a68 100644
--- a/src/hd_active/ui/system_tray_icon.py
+++ b/src/hd_active/ui/system_tray_icon.py
@@ -2,11 +2,11 @@
 
 from PySide6.QtWidgets import QApplication, QMenu, QMessageBox, QSystemTrayIcon
 
-from src.hd_active import __version__
-from src.hd_active.hd_active import HdActive
-from src.hd_active.hd_active_config import HdActiveConfig
-from src.hd_active.ui.settings_dialog import SettingsDialog
-from src.hd_active.utils import is_truthy
+from .. import __version__
+from ..hd_active import HdActive
+from ..hd_active_config import HdActiveConfig
+from ..utils import is_truthy
+from .settings_dialog import SettingsDialog
 
 HD_ACTION_DEBUG = is_truthy(os.getenv('HD_ACTION_DEBUG', 'True'))
 """
diff --git a/tasks.py b/tasks.py
index 59d8831..9170caf 100644
--- a/tasks.py
+++ b/tasks.py
@@ -1,4 +1,5 @@
 import os
+import sys
 from pathlib import Path
 
 from invoke import Collection, Exit, task
@@ -14,6 +15,9 @@
 """Source code for the this project's package."""
 ASSETS_DIR = PROJECT_ROOT / 'assets'
 
+if str(PROJECT_SOURCE_DIR) not in sys.path:
+    sys.path.insert(0, str(PROJECT_SOURCE_DIR))
+
 # Requirements files
 REQUIREMENTS_MAIN = 'main'
 REQUIREMENTS_FILES = {
@@ -123,9 +127,9 @@ def _get_os_name():
 
 
 def _get_build_app_files() -> tuple[Path, Path]:
-    import src.hd_active
+    import hd_active
 
-    version = src.hd_active.__version__
+    version = hd_active.__version__
 
     # Assumes the distribution directory is empty prior to creating the app
     files = [f for f in BUILD_DIST_APP_DIR.glob('*') if f.is_file() and f.suffix.lower() != '.zip']
@@ -280,7 +284,19 @@ def _update_imports():
             file_path = root_path / file
 
             regex_replace = [
-                (r'''^( *from[ ]+)(\.)( .*)''', module),  # from . import <module>
+                (r'''^( *from[ ]+)(\.{1})( .*)''', module),  # from . import <module>
+                (
+                    r'''^( *from[ ]+)(\.{2})( .*)''',
+                    '.'.join(module.split('.')[:-1]),
+                ),  # from .. import <module>
+                (
+                    r'''^( *from[ ]+)(\.{3})( .*)''',
+                    '.'.join(module.split('.')[:-2]),
+                ),  # from ... import <module>
+                (
+                    r'''^( *from[ ]+)(\.{3})(.*)''',
+                    '.'.join(module.split('.')[:-2]) + '.',
+                ),
                 (
                     r'''^( *from[ ]+)(\.{2})(.*)''',
                     '.'.join(module.split('.')[:-1]) + '.',
@@ -583,10 +599,10 @@ def build_upload(c, label: str = 'none'):
     """
     from packaging.version import Version
 
-    import src.hd_active
+    import hd_active
 
     _, zip_file = _get_build_app_files()
-    app_version = Version(src.hd_active.__version__)
+    app_version = Version(hd_active.__version__)
 
     if not zip_file.exists():
         raise Exit(
@@ -644,7 +660,7 @@ def build_run(c):
             raise Exit('Multiple executables found.')
         c.run(str(exes[0]))
     elif os_name == 'mac':
-        app_file, _, _ = _get_build_app_files()
+        app_file, _ = _get_build_app_files()
         c.run(str(app_file))
     elif os_name == 'linux':
         raise Exit('Running on Linux not yet implemented.')
@@ -756,12 +772,17 @@ def lint_mypy(c, path='.'):
     c.run(f'mypy {path}')
 
 
-@task(lint_isort, lint_black, lint_flake8, lint_mypy)
+@task
 def lint_all(c):
     """
     Run all linters.
     Config for each of the tools is in ``pyproject.toml`` and ``setup.cfg``.
     """
+    lint_isort(c)
+    lint_black(c)
+    lint_flake8(c)
+    lint_mypy(c, 'src')
+    lint_mypy(c, 'tests')
     print('Done')
 
 
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..3fcbdc8
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,8 @@
+# Ensure the 'src' directory is on sys.path so tests can import 'hd_active' without installation.
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+SOURCE = ROOT / 'src'
+if str(SOURCE) not in sys.path:
+    sys.path.insert(0, str(SOURCE))
diff --git a/tests/test_hd_active.py b/tests/test_hd_active.py
index 9670c30..6a65ae4 100644
--- a/tests/test_hd_active.py
+++ b/tests/test_hd_active.py
@@ -6,8 +6,8 @@
 
 import pytest
 
-from src.hd_active.hd_action_state import HdActionState
-from src.hd_active.hd_active import HdActive
+from hd_active.hd_action_state import HdActionState
+from hd_active.hd_active import HdActive
 
 WAIT = 0.1
 WAIT_TEST = 2 * WAIT
@@ -22,7 +22,7 @@ def __init__(self, drive_paths=None, run=False, wait=WAIT):
         super().__init__(drive_paths, run, wait=wait)
 
 
-@patch('src.hd_active.hd_active.HdActive._write_hd', return_value=1000)
+@patch('hd_active.hd_active.HdActive._write_hd', return_value=1000)
 class TestHdActive:
     def test_instantiate_not_started(self, mock_write_hd):
         hd_active = HdActiveTest(drive_paths=['z'], run=False)
diff --git a/tests/test_hd_active_config.py b/tests/test_hd_active_config.py
index 40e4052..619b082 100644
--- a/tests/test_hd_active_config.py
+++ b/tests/test_hd_active_config.py
@@ -3,7 +3,7 @@
 
 import pytest
 
-from src.hd_active.hd_active_config import HdActiveConfig
+from hd_active.hd_active_config import HdActiveConfig
 
 
 @pytest.fixture
@@ -19,7 +19,7 @@ def config_file(request, tmp_path) -> Tuple[str, List[str]]:
     return str(file), request.param[1]
 
 
-@patch('src.hd_active.hd_active_config.configparser.ConfigParser.read')
+@patch('hd_active.hd_active_config.configparser.ConfigParser.read')
 def test_defaults(read_mock):
     """
     Skip reading file (so defaults are not overwritten) and verify defaults.
diff --git a/tests/test_utils.py b/tests/test_utils.py
index e99d3c1..7351472 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1,6 +1,6 @@
 import pytest
 
-from src.hd_active.utils import ASSETS_ROOT, PROJECT_ROOT, get_asset, is_truthy
+from hd_active.utils import ASSETS_ROOT, PROJECT_ROOT, get_asset, is_truthy
 
 
 class TestGlobals: