diff --git a/README.md b/README.md
index 9f916a0..4ee05b9 100644
--- a/README.md
+++ b/README.md
@@ -76,6 +76,13 @@ found in `setup.cfg` loosening the rules in isolated cases, notably
 `user_keymaps` (which is *also* not subject to Black formatting for reasons
 documented in `pyproject.toml`).
 
+## Tests
+
+Unit tests within the `tests` folder mock various CicuitPython modules to allow
+them to be executed in a desktop development environment.
+
+Execute tests using the command `python -m unittest`.
+
 ## License, Copyright, and Legal
 
 All software in this repository is licensed under the [GNU Public License,
diff --git a/kmk/hid.py b/kmk/hid.py
index 8684ceb..56b0329 100644
--- a/kmk/hid.py
+++ b/kmk/hid.py
@@ -53,6 +53,7 @@ class AbstractHID:
     REPORT_BYTES = 8
 
     def __init__(self, **kwargs):
+        self._prev_evt = bytearray(self.REPORT_BYTES)
         self._evt = bytearray(self.REPORT_BYTES)
         self.report_device = memoryview(self._evt)[0:1]
         self.report_device[0] = HIDReportTypes.KEYBOARD
@@ -125,7 +126,10 @@ class AbstractHID:
         pass
 
     def send(self):
-        self.hid_send(self._evt)
+        changed = not self._evt.startswith(self._prev_evt)
+        if changed:
+            self._prev_evt[:] = self._evt
+            self.hid_send(self._evt)
 
         return self
 
diff --git a/kmk/kmk_keyboard.py b/kmk/kmk_keyboard.py
index ea1fe3f..b643de8 100644
--- a/kmk/kmk_keyboard.py
+++ b/kmk/kmk_keyboard.py
@@ -373,6 +373,11 @@ class KMKKeyboard:
                     print('Failed to run post hid function in extension: ', err, ext)
 
     def go(self, hid_type=HIDModes.USB, secondary_hid_type=None, **kwargs):
+        self._init(hid_type=hid_type, secondary_hid_type=secondary_hid_type, **kwargs)
+        while True:
+            self._main_loop()
+
+    def _init(self, hid_type=HIDModes.USB, secondary_hid_type=None, **kwargs):
         self._go_args = kwargs
         self.hid_type = hid_type
         self.secondary_hid_type = secondary_hid_type
@@ -398,46 +403,44 @@ class KMKKeyboard:
 
         self._print_debug_cycle(init=True)
 
-        while True:
-            self.current_key = None
-            self.state_changed = False
-            self.sandbox.active_layers = self.active_layers.copy()
+    def _main_loop(self):
+        self.current_key = None
+        self.state_changed = False
+        self.sandbox.active_layers = self.active_layers.copy()
 
-            self.before_matrix_scan()
+        self.before_matrix_scan()
 
-            self.matrix_update = (
-                self.sandbox.matrix_update
-            ) = self.matrix.scan_for_changes()
-            self.sandbox.secondary_matrix_update = self.secondary_matrix_update
+        self.matrix_update = self.sandbox.matrix_update = self.matrix.scan_for_changes()
+        self.sandbox.secondary_matrix_update = self.secondary_matrix_update
 
-            self.after_matrix_scan()
+        self.after_matrix_scan()
 
-            self._handle_matrix_report(self.secondary_matrix_update)
-            self.secondary_matrix_update = None
-            self._handle_matrix_report(self.matrix_update)
-            self.matrix_update = None
+        self._handle_matrix_report(self.secondary_matrix_update)
+        self.secondary_matrix_update = None
+        self._handle_matrix_report(self.matrix_update)
+        self.matrix_update = None
 
-            self.before_hid_send()
+        self.before_hid_send()
 
+        if self.hid_pending:
+            self._send_hid()
+
+        self._old_timeouts_len = len(self._timeouts)
+        self._process_timeouts()
+        self._new_timeouts_len = len(self._timeouts)
+
+        if self._old_timeouts_len != self._new_timeouts_len:
+            self.state_changed = True
             if self.hid_pending:
                 self._send_hid()
 
-            self._old_timeouts_len = len(self._timeouts)
-            self._process_timeouts()
-            self._new_timeouts_len = len(self._timeouts)
+        self.after_hid_send()
 
-            if self._old_timeouts_len != self._new_timeouts_len:
-                self.state_changed = True
-                if self.hid_pending:
-                    self._send_hid()
+        if self._trigger_powersave_enable:
+            self.powersave_enable()
 
-            self.after_hid_send()
+        if self._trigger_powersave_disable:
+            self.powersave_disable()
 
-            if self._trigger_powersave_enable:
-                self.powersave_enable()
-
-            if self._trigger_powersave_disable:
-                self.powersave_disable()
-
-            if self.state_changed:
-                self._print_debug_cycle()
+        if self.state_changed:
+            self._print_debug_cycle()
diff --git a/kmk/modules/holdtap.py b/kmk/modules/holdtap.py
index 840c4ee..4145e8f 100644
--- a/kmk/modules/holdtap.py
+++ b/kmk/modules/holdtap.py
@@ -44,8 +44,7 @@ class HoldTap(Module):
                     self.ht_activate_on_interrupt(
                         key, keyboard, *state.args, **state.kwargs
                     )
-                    if keyboard.hid_pending:
-                        keyboard._send_hid()
+                    keyboard._send_hid()
         return current_key
 
     def before_hid_send(self, keyboard):
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e17e7e5
--- /dev/null
+++ b/tests/__init__.py
@@ -0,0 +1,3 @@
+from tests.mocks import init_circuit_python_modules_mocks
+
+init_circuit_python_modules_mocks()
diff --git a/tests/keyboard_test.py b/tests/keyboard_test.py
new file mode 100644
index 0000000..0caff80
--- /dev/null
+++ b/tests/keyboard_test.py
@@ -0,0 +1,94 @@
+import random
+import time
+from functools import reduce
+from unittest.mock import Mock, patch
+
+from kmk.hid import HIDModes
+from kmk.keys import ModifierKey
+from kmk.kmk_keyboard import KMKKeyboard
+from kmk.matrix import DiodeOrientation
+
+
+class DigitalInOut(Mock):
+    value = False
+
+
+class KeyboardTest:
+    def __init__(
+        self, modules, keymap, keyboard_debug_enabled=False, debug_enabled=False
+    ):
+        self.debug_enabled = debug_enabled
+
+        self.keyboard = KMKKeyboard()
+        self.keyboard.debug_enabled = keyboard_debug_enabled
+
+        self.keyboard.modules = modules
+
+        self.pins = tuple(DigitalInOut() for k in keymap[0])
+
+        self.keyboard.col_pins = (DigitalInOut(),)
+        self.keyboard.row_pins = self.pins
+        self.keyboard.diode_orientation = DiodeOrientation.COL2ROW
+        self.keyboard.keymap = keymap
+
+        self.keyboard._init(hid_type=HIDModes.NOOP)
+
+    @patch('kmk.hid.AbstractHID.hid_send')
+    def test(self, testname, key_events, assert_hid_reports, hid_send):
+        if self.debug_enabled:
+            print(testname, key_events, assert_hid_reports)
+
+        hid_send_call_arg_list = []
+        hid_send.side_effect = lambda hid_report: hid_send_call_arg_list.append(
+            hid_report[1:]
+        )
+
+        for e in key_events:
+            if isinstance(e, int):
+                starttime_ms = time.time_ns() // 1_000_000
+                while time.time_ns() // 1_000_000 - starttime_ms < e:
+                    self.do_main_loop()
+            else:
+                key_pos = e[0]
+                is_pressed = e[1]
+                self.pins[key_pos].value = is_pressed
+                self.do_main_loop()
+
+        if self.debug_enabled:
+            for hid_report in hid_send_call_arg_list:
+                print(hid_report)
+
+        for i, hid_report in enumerate(
+            hid_send_call_arg_list[-len(assert_hid_reports) :]
+        ):
+            hid_report_keys = {code for code in hid_report[2:] if code != 0}
+            assert_keys = {
+                k.code for k in assert_hid_reports[i] if not isinstance(k, ModifierKey)
+            }
+            if self.debug_enabled:
+                print(
+                    'assert keys:',
+                    hid_report_keys == assert_keys,
+                    hid_report_keys,
+                    assert_keys,
+                )
+            assert hid_report_keys == assert_keys
+
+            hid_report_modifiers = hid_report[0]
+            assert_modifiers = reduce(
+                lambda mod, all_mods: all_mods | mod,
+                {k.code for k in assert_hid_reports[i] if isinstance(k, ModifierKey)},
+                0,
+            )
+            if self.debug_enabled:
+                print(
+                    'assert mods:',
+                    hid_report_modifiers == assert_modifiers,
+                    hid_report_modifiers,
+                    assert_modifiers,
+                )
+            assert hid_report_modifiers == assert_modifiers
+
+    def do_main_loop(self):
+        for i in range(random.randint(5, 50)):
+            self.keyboard._main_loop()
diff --git a/tests/mocks.py b/tests/mocks.py
new file mode 100644
index 0000000..2f8afc1
--- /dev/null
+++ b/tests/mocks.py
@@ -0,0 +1,20 @@
+import sys
+import time
+from unittest.mock import Mock
+
+
+def init_circuit_python_modules_mocks():
+    sys.modules['usb_hid'] = Mock()
+    sys.modules['digitalio'] = Mock()
+    sys.modules['neopixel'] = Mock()
+    sys.modules['pulseio'] = Mock()
+    sys.modules['busio'] = Mock()
+    sys.modules['microcontroller'] = Mock()
+    sys.modules['board'] = Mock()
+    sys.modules['storage'] = Mock()
+
+    sys.modules['micropython'] = Mock()
+    sys.modules['micropython'].const = lambda x: x
+
+    sys.modules['supervisor'] = Mock()
+    sys.modules['supervisor'].ticks_ms = lambda: time.time_ns() // 1_000_000
diff --git a/tests/test_hold_tap.py b/tests/test_hold_tap.py
new file mode 100644
index 0000000..01b8794
--- /dev/null
+++ b/tests/test_hold_tap.py
@@ -0,0 +1,106 @@
+import unittest
+
+from kmk.keys import KC
+from kmk.modules.layers import Layers
+from kmk.modules.modtap import ModTap
+from tests.keyboard_test import KeyboardTest
+
+
+class TestHoldTap(unittest.TestCase):
+    def test_basic_kmk_keyboard(self):
+        keyboard = KeyboardTest(
+            [Layers(), ModTap()],
+            [
+                [KC.MT(KC.A, KC.LCTL), KC.LT(1, KC.B), KC.C, KC.D],
+                [KC.N1, KC.N2, KC.N3, KC.N4],
+            ],
+            debug_enabled=False,
+        )
+
+        keyboard.test('MT tap behaviour', [(0, True), 100, (0, False)], [{KC.A}, {}])
+
+        keyboard.test(
+            'MT hold behaviour', [(0, True), 350, (0, False)], [{KC.LCTL}, {}]
+        )
+
+        # TODO test multiple mods being held
+
+        # MT
+        keyboard.test(
+            'MT within tap time sequential -> tap behavior',
+            [(0, True), 100, (0, False), (3, True), (3, False)],
+            [{KC.A}, {}, {KC.D}, {}],
+        )
+
+        keyboard.test(
+            'MT within tap time rolling -> tap behavior',
+            [(0, True), 100, (3, True), 250, (0, False), (3, False)],
+            [{KC.A}, {KC.A, KC.D}, {KC.D}, {}],
+        )
+
+        keyboard.test(
+            'MT within tap time nested -> tap behavior',
+            [(0, True), 100, (3, True), (3, False), 250, (0, False)],
+            [{KC.A}, {KC.A, KC.D}, {KC.A}, {}],
+        )
+
+        keyboard.test(
+            'MT after tap time sequential -> hold behavior',
+            [(0, True), 350, (0, False), (3, True), (3, False)],
+            [{KC.LCTL}, {}, {KC.D}, {}],
+        )
+
+        keyboard.test(
+            'MT after tap time rolling -> hold behavior',
+            [(0, True), 350, (3, True), (0, False), (3, False)],
+            [{KC.LCTL}, {KC.LCTL, KC.D}, {KC.D}, {}],
+        )
+
+        keyboard.test(
+            'MT after tap time nested -> hold behavior',
+            [(0, True), 350, (3, True), (3, False), (0, False)],
+            [{KC.LCTL}, {KC.LCTL, KC.D}, {KC.LCTL}, {}],
+        )
+
+        # LT
+        keyboard.test(
+            'LT within tap time sequential -> tap behavior',
+            [(1, True), 100, (1, False), (3, True), (3, False)],
+            [{KC.B}, {}, {KC.D}, {}],
+        )
+
+        keyboard.test(
+            'LT within tap time rolling -> tap behavior',
+            [(1, True), 100, (3, True), 250, (1, False), (3, False)],
+            [{KC.B}, {KC.B, KC.D}, {KC.D}, {}],
+        )
+
+        keyboard.test(
+            'LT within tap time nested -> tap behavior',
+            [(1, True), 100, (3, True), (3, False), 250, (1, False)],
+            [{KC.B}, {KC.B, KC.D}, {KC.B}, {}],
+        )
+
+        keyboard.test(
+            'LT after tap time sequential -> hold behavior',
+            [(1, True), 350, (1, False), (3, True), (3, False)],
+            [{KC.D}, {}],
+        )
+
+        keyboard.test(
+            'LT after tap time rolling -> hold behavior',
+            [(1, True), 350, (3, True), (1, False), (3, False)],
+            [{KC.N4}, {}],
+        )
+
+        keyboard.test(
+            'LT after tap time nested -> hold behavior',
+            [(1, True), 350, (3, True), (3, False), (1, False)],
+            [{KC.N4}, {}],
+        )
+
+        # TODO test TT
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/tests/test_kmk_keyboard.py b/tests/test_kmk_keyboard.py
new file mode 100644
index 0000000..237e5f3
--- /dev/null
+++ b/tests/test_kmk_keyboard.py
@@ -0,0 +1,15 @@
+import unittest
+
+from kmk.keys import KC
+from tests.keyboard_test import KeyboardTest
+
+
+class TestKmkKeyboard(unittest.TestCase):
+    def test_basic_kmk_keyboard(self):
+        keyboard = KeyboardTest([], [[KC.N1, KC.N2, KC.N3, KC.N4]])
+
+        keyboard.test('Simple key press', [(0, True), (0, False)], [{KC.N1}, {}])
+
+
+if __name__ == '__main__':
+    unittest.main()