diff --git a/go.mod b/go.mod
index f7c13dd..2388397 100644
--- a/go.mod
+++ b/go.mod
@@ -5,4 +5,11 @@ go 1.24.4
 require (
 	github.com/goccy/go-yaml v1.18.0
 	github.com/holoplot/go-evdev v0.0.0-20240306072622-217e18f17db1
+	github.com/stretchr/testify v1.10.0
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
diff --git a/go.sum b/go.sum
index 69c3bf7..539dcc7 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +1,14 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/goccy/go-yaml v1.18.0 h1:8W7wMFS12Pcas7KU+VVkaiCng+kG8QiFeFwzFb+rwuw=
 github.com/goccy/go-yaml v1.18.0/go.mod h1:XBurs7gK8ATbW4ZPGKgcbrY1Br56PdM69F7LkFRi1kA=
 github.com/holoplot/go-evdev v0.0.0-20240306072622-217e18f17db1 h1:92OsBIf5KB1Tatx+uUGOhah73jyNUrt7DmfDRXXJ5Xo=
 github.com/holoplot/go-evdev v0.0.0-20240306072622-217e18f17db1/go.mod h1:iHAf8OIncO2gcQ8XOjS7CMJ2aPbX2Bs0wl5pZyanEqk=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
+github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/internal/mappingrules/interfaces.go b/internal/mappingrules/interfaces.go
new file mode 100644
index 0000000..ef54fbf
--- /dev/null
+++ b/internal/mappingrules/interfaces.go
@@ -0,0 +1,28 @@
+package mappingrules
+
+import "github.com/holoplot/go-evdev"
+
+type MappingRule interface {
+	MatchEvent(*evdev.InputDevice, *evdev.InputEvent, *string) *evdev.InputEvent
+	OutputName() string
+}
+
+// RuleTargets represent either a device input to match on, or an output to produce.
+// Some RuleTarget types may work via side effects, such as RuleTargetModeSelect.
+type RuleTarget interface {
+	// NormalizeValue takes the raw input value and possibly modifies it based on the Target settings.
+	// (e.g., inverting the value if Inverted == true)
+	NormalizeValue(int32) int32
+
+	// CreateEvent typically takes the (probably normalized) value and returns an event that can be emitted
+	// on a virtual device.
+	//
+	// For RuleTargetModeSelect, this method modifies the active mode and returns nil.
+	//
+	// TODO: should we normalize inside this function to simplify the interface?
+	CreateEvent(int32, *string) *evdev.InputEvent
+
+	GetCode() evdev.EvCode
+	GetDeviceName() string
+	GetDevice() *evdev.InputDevice
+}
diff --git a/internal/mappingrules/matching_test.go b/internal/mappingrules/matching_test.go
index e7e6e3b..00a6da5 100644
--- a/internal/mappingrules/matching_test.go
+++ b/internal/mappingrules/matching_test.go
@@ -4,63 +4,91 @@ import (
 	"testing"
 
 	"github.com/holoplot/go-evdev"
+	"github.com/stretchr/testify/suite"
 )
 
-func TestSimpleRuleMatchEvent(t *testing.T) {
-	inputDevice := &evdev.InputDevice{}
-	wrongInputDevice := &evdev.InputDevice{}
-	outputDevice := &evdev.InputDevice{}
+type SimpleMappingRuleTests struct {
+	suite.Suite
+	inputDevice      *evdev.InputDevice
+	wrongInputDevice *evdev.InputDevice
+	outputDevice     *evdev.InputDevice
+	mode             *string
+	sampleRule       *SimpleMappingRule
+	invertedRule     *SimpleMappingRule
+}
 
-	rule := &SimpleMappingRule{
-		MappingRuleBase: MappingRuleBase{
-			Output: &RuleTargetButton{
-				RuleTargetBase{
-					DeviceName: "test_output",
-					Device:     outputDevice,
-					Code:       evdev.BTN_TRIGGER,
-				},
-			},
-			Modes: []string{"*"},
-		},
-		Input: &RuleTargetButton{
-			RuleTargetBase{
-				DeviceName: "test_input",
-				Device:     inputDevice,
-				Code:       evdev.BTN_TRIGGER,
-			},
-		},
-	}
+func (t *SimpleMappingRuleTests) SetupTest() {
+	t.inputDevice = &evdev.InputDevice{}
+	t.wrongInputDevice = &evdev.InputDevice{}
+	t.outputDevice = &evdev.InputDevice{}
 	mode := "*"
+	t.mode = &mode
 
+	// TODO: implement a constructor function...
+	t.sampleRule = &SimpleMappingRule{
+		MappingRuleBase: MappingRuleBase{
+			Output: NewRuleTargetButton("", t.outputDevice, evdev.BTN_TRIGGER, false),
+			Modes:  []string{"*"},
+		},
+		Input: NewRuleTargetButton("", t.inputDevice, evdev.BTN_TRIGGER, false),
+	}
+
+	t.invertedRule = &SimpleMappingRule{
+		MappingRuleBase: MappingRuleBase{
+			Output: NewRuleTargetButton("", t.outputDevice, evdev.BTN_TRIGGER, false),
+			Modes:  []string{"*"},
+		},
+		Input: NewRuleTargetButton("", t.inputDevice, evdev.BTN_TRIGGER, true),
+	}
+}
+
+func (t *SimpleMappingRuleTests) TestMatchEvent() {
 	// A matching input event should produce an output event
-	event := rule.MatchEvent(inputDevice, &evdev.InputEvent{Code: evdev.BTN_TRIGGER, Value: 1}, &mode)
-	outputEvent := &evdev.InputEvent{
+	correctOutput := &evdev.InputEvent{
 		Type:  evdev.EV_KEY,
 		Code:  evdev.BTN_TRIGGER,
 		Value: 1,
 	}
 
-	if event == nil || *event != *outputEvent {
-		t.Errorf("Expected event to match %v, but got %v", outputEvent, event)
-	}
-
-	// if event.Type != outputEvent.Type ||
-	// 	event.Code != outputEvent.Code ||
-	// 	event.Value != outputEvent.Value {
-	// 	t.Errorf("Expected event to match %v, but got %v", outputEvent, event)
-	// }
+	event := t.sampleRule.MatchEvent(
+		t.inputDevice,
+		&evdev.InputEvent{Code: evdev.BTN_TRIGGER, Value: 1}, t.mode)
+	t.EqualValues(correctOutput, event)
 
 	// An input event from the wrong device should produce a nil event
-	event = rule.MatchEvent(wrongInputDevice, &evdev.InputEvent{Code: evdev.BTN_TRIGGER, Value: 1}, &mode)
-	if event != nil {
-		t.Errorf("Expected event not to match, but got non-nil event %v", event)
-	}
+	event = t.sampleRule.MatchEvent(
+		t.wrongInputDevice,
+		&evdev.InputEvent{Code: evdev.BTN_TRIGGER, Value: 1}, t.mode)
+	t.Nil(event)
 
-	// An input event from the wrong device should produce a nil event
-	event = rule.MatchEvent(wrongInputDevice, &evdev.InputEvent{Code: evdev.BTN_TRIGGER, Value: 1}, &mode)
-	if event != nil {
-		t.Errorf("Expected event not to match, but got non-nil event %v", event)
-	}
-
-	// TODO: test inversion, and everything else...
+	// An input event from the wrong button should produce a nil event
+	event = t.sampleRule.MatchEvent(
+		t.inputDevice,
+		&evdev.InputEvent{Code: evdev.BTN_TOP, Value: 1}, t.mode)
+	t.Nil(event)
+}
+
+func (t *SimpleMappingRuleTests) TestMatchEventInverted() {
+	// A matching input event should produce an output event
+	correctOutput := &evdev.InputEvent{
+		Type: evdev.EV_KEY,
+		Code: evdev.BTN_TRIGGER,
+	}
+
+	// Should get the opposite value out that we send in
+	correctOutput.Value = 0
+	event := t.invertedRule.MatchEvent(
+		t.inputDevice,
+		&evdev.InputEvent{Code: evdev.BTN_TRIGGER, Value: 1}, t.mode)
+	t.EqualValues(correctOutput, event)
+
+	correctOutput.Value = 1
+	event = t.invertedRule.MatchEvent(
+		t.inputDevice,
+		&evdev.InputEvent{Code: evdev.BTN_TRIGGER, Value: 0}, t.mode)
+	t.EqualValues(correctOutput, event)
+}
+
+func TestRunnerMatching(t *testing.T) {
+	suite.Run(t, new(SimpleMappingRuleTests))
 }
diff --git a/internal/mappingrules/rule_target_axis.go b/internal/mappingrules/rule_target_axis.go
new file mode 100644
index 0000000..938ad41
--- /dev/null
+++ b/internal/mappingrules/rule_target_axis.go
@@ -0,0 +1,61 @@
+package mappingrules
+
+import (
+	"github.com/holoplot/go-evdev"
+)
+
+type RuleTargetAxis struct {
+	RuleTargetBase
+	AxisStart   int32
+	AxisEnd     int32
+	Sensitivity float64
+}
+
+func NewRuleTargetAxis(device_name string,
+	device *evdev.InputDevice,
+	code evdev.EvCode,
+	inverted bool,
+	axis_start int32,
+	axis_end int32,
+	sensitivity float64) *RuleTargetAxis {
+
+	return &RuleTargetAxis{
+		RuleTargetBase: NewRuleTargetBase(device_name, device, code, inverted),
+		AxisStart:      axis_start,
+		AxisEnd:        axis_end,
+		Sensitivity:    sensitivity,
+	}
+}
+
+func (target *RuleTargetAxis) NormalizeValue(value int32) int32 {
+	if !target.Inverted {
+		return value
+	}
+
+	axisRange := target.AxisEnd - target.AxisStart
+	axisMid := target.AxisEnd - axisRange/2
+	delta := value - axisMid
+	if delta < 0 {
+		delta = -delta
+	}
+
+	if value < axisMid {
+		return axisMid + delta
+	} else if value > axisMid {
+		return axisMid - delta
+	}
+
+	// If we reach here, we're either exactly at the midpoint or something
+	// strange has happened. Either way, just return the value.
+	return value
+}
+
+func (target *RuleTargetAxis) CreateEvent(value int32, mode *string) *evdev.InputEvent {
+	// TODO: we can use the axis begin/end to decide whether to emit the event
+	// TODO: oh no we need center deadzones actually...
+	return &evdev.InputEvent{
+		Type:  evdev.EV_ABS,
+		Code:  target.Code,
+		Value: value,
+	}
+}
diff --git a/internal/mappingrules/rule_target_base.go b/internal/mappingrules/rule_target_base.go
new file mode 100644
index 0000000..7d03130
--- /dev/null
+++ b/internal/mappingrules/rule_target_base.go
@@ -0,0 +1,35 @@
+package mappingrules
+
+import "github.com/holoplot/go-evdev"
+
+type RuleTargetBase struct {
+	DeviceName string
+	Device     *evdev.InputDevice
+	Code       evdev.EvCode
+	Inverted   bool
+}
+
+func NewRuleTargetBase(device_name string,
+	device *evdev.InputDevice,
+	code evdev.EvCode,
+	inverted bool) RuleTargetBase {
+
+	return RuleTargetBase{
+		DeviceName: device_name,
+		Device:     device,
+		Code:       code,
+		Inverted:   inverted,
+	}
+}
+
+func (target *RuleTargetBase) GetCode() evdev.EvCode {
+	return target.Code
+}
+
+func (target *RuleTargetBase) GetDeviceName() string {
+	return target.DeviceName
+}
+
+func (target *RuleTargetBase) GetDevice() *evdev.InputDevice {
+	return target.Device
+}
diff --git a/internal/mappingrules/rule_target_button.go b/internal/mappingrules/rule_target_button.go
new file mode 100644
index 0000000..b34b498
--- /dev/null
+++ b/internal/mappingrules/rule_target_button.go
@@ -0,0 +1,31 @@
+package mappingrules
+
+import "github.com/holoplot/go-evdev"
+
+type RuleTargetButton struct {
+	RuleTargetBase
+}
+
+func NewRuleTargetButton(device_name string, device *evdev.InputDevice, code evdev.EvCode, inverted bool) *RuleTargetButton {
+	return &RuleTargetButton{
+		RuleTargetBase: NewRuleTargetBase(device_name, device, code, inverted),
+	}
+}
+
+func (target *RuleTargetButton) NormalizeValue(value int32) int32 {
+	if target.Inverted {
+		if value == 0 {
+			return 1
+		}
+		return 0
+	}
+	return value
+}
+
+func (target *RuleTargetButton) CreateEvent(value int32, mode *string) *evdev.InputEvent {
+	return &evdev.InputEvent{
+		Type:  evdev.EV_KEY,
+		Code:  target.Code,
+		Value: value,
+	}
+}
diff --git a/internal/mappingrules/rule_target_modeselect.go b/internal/mappingrules/rule_target_modeselect.go
new file mode 100644
index 0000000..7ed4332
--- /dev/null
+++ b/internal/mappingrules/rule_target_modeselect.go
@@ -0,0 +1,41 @@
+package mappingrules
+
+import (
+	"slices"
+
+	"git.annabunches.net/annabunches/joyful/internal/logger"
+	"github.com/holoplot/go-evdev"
+)
+
+type RuleTargetModeSelect struct {
+	RuleTargetBase
+	ModeSelect []string
+}
+
+func NewRuleTargetModeSelect(modes []string) *RuleTargetModeSelect {
+	return &RuleTargetModeSelect{
+		RuleTargetBase: NewRuleTargetBase("", nil, 0, false),
+		ModeSelect:     modes,
+	}
+}
+
+// RuleTargetModeSelect doesn't make sense as an input type
+func (target *RuleTargetModeSelect) NormalizeValue(value int32) int32 {
+	return -1
+}
+
+func (target *RuleTargetModeSelect) CreateEvent(value int32, mode *string) *evdev.InputEvent {
+	if value == 0 {
+		return nil
+	}
+
+	index := 0
+	if currentMode := slices.Index(target.ModeSelect, *mode); currentMode != -1 {
+		// find the next mode
+		index = (currentMode + 1) % len(target.ModeSelect)
+	}
+
+	*mode = target.ModeSelect[index]
+	logger.Logf("Mode changed to '%s'", *mode)
+	return nil
+}
diff --git a/internal/mappingrules/targets.go b/internal/mappingrules/targets.go
deleted file mode 100644
index bc2129c..0000000
--- a/internal/mappingrules/targets.go
+++ /dev/null
@@ -1,90 +0,0 @@
-package mappingrules
-
-import (
-	"slices"
-
-	"git.annabunches.net/annabunches/joyful/internal/logger"
-	"github.com/holoplot/go-evdev"
-)
-
-func (target *RuleTargetBase) GetCode() evdev.EvCode {
-	return target.Code
-}
-
-func (target *RuleTargetBase) GetDeviceName() string {
-	return target.DeviceName
-}
-
-func (target *RuleTargetBase) GetDevice() *evdev.InputDevice {
-	return target.Device
-}
-
-func (target *RuleTargetButton) NormalizeValue(value int32) int32 {
-	if target.Inverted {
-		if value == 0 {
-			return 1
-		}
-		return 0
-	}
-	return value
-}
-
-func (target *RuleTargetButton) CreateEvent(value int32, mode *string) *evdev.InputEvent {
-	return &evdev.InputEvent{
-		Type:  evdev.EV_KEY,
-		Code:  target.Code,
-		Value: value,
-	}
-}
-
-func (target *RuleTargetAxis) NormalizeValue(value int32) int32 {
-	if !target.Inverted {
-		return value
-	}
-
-	axisRange := target.AxisEnd - target.AxisStart
-	axisMid := target.AxisEnd - axisRange/2
-	delta := value - axisMid
-	if delta < 0 {
-		delta = -delta
-	}
-
-	if value < axisMid {
-		return axisMid + delta
-	} else if value > axisMid {
-		return axisMid - delta
-	}
-
-	// If we reach here, we're either exactly at the midpoint or something
-	// strange has happened. Either way, just return the value.
-	return value
-}
-
-func (target *RuleTargetAxis) CreateEvent(value int32, mode *string) *evdev.InputEvent {
-	return &evdev.InputEvent{
-		Type:  evdev.EV_ABS,
-		Code:  target.Code,
-		Value: value,
-	}
-}
-
-// RuleTargetModeSelect doesn't make sense as an input type
-func (target *RuleTargetModeSelect) NormalizeValue(value int32) int32 {
-	return -1
-}
-
-func (target *RuleTargetModeSelect) CreateEvent(value int32, mode *string) *evdev.InputEvent {
-	if value == 0 {
-		return nil
-	}
-
-	index := 0
-	if currentMode := slices.Index(target.ModeSelect, *mode); currentMode != -1 {
-		// find the next mode
-		index = (currentMode + 1) % len(target.ModeSelect)
-	}
-
-	*mode = target.ModeSelect[index]
-	logger.Logf("Mode changed to '%s'", *mode)
-	return nil
-}
diff --git a/internal/mappingrules/types.go b/internal/mappingrules/types.go
index e7aa72f..35b1c77 100644
--- a/internal/mappingrules/types.go
+++ b/internal/mappingrules/types.go
@@ -2,15 +2,8 @@ package mappingrules
 
 import (
 	"time"
-
-	"github.com/holoplot/go-evdev"
 )
 
-type MappingRule interface {
-	MatchEvent(*evdev.InputDevice, *evdev.InputEvent, *string) *evdev.InputEvent
-	OutputName() string
-}
-
 type MappingRuleBase struct {
 	Name   string
 	Output RuleTarget
@@ -43,46 +36,3 @@ type ProportionalAxisMappingRule struct {
 	Output    RuleTarget
 	LastEvent time.Time
 }
-
-// RuleTargets represent either a device input to match on, or an output to produce.
-// Some RuleTarget types may work via side effects, such as RuleTargetModeSelect.
-type RuleTarget interface {
-	// NormalizeValue takes the raw input value and possibly modifies it based on the Target settings.
-	// (e.g., inverting the value if Inverted == true)
-	NormalizeValue(int32) int32
-
-	// CreateEvent typically takes the (probably normalized) value and returns an event that can be emitted
-	// on a virtual device.
-	//
-	// For RuleTargetModeSelect, this method modifies the active mode and returns nil.
-	//
-	// TODO: should we normalize inside this function to simplify the interface?
-	CreateEvent(int32, *string) *evdev.InputEvent
-
-	GetCode() evdev.EvCode
-	GetDeviceName() string
-	GetDevice() *evdev.InputDevice
-}
-
-type RuleTargetBase struct {
-	DeviceName string
-	Device     *evdev.InputDevice
-	Code       evdev.EvCode
-	Inverted   bool
-}
-
-type RuleTargetButton struct {
-	RuleTargetBase
-}
-
-type RuleTargetAxis struct {
-	RuleTargetBase
-	AxisStart   int32
-	AxisEnd     int32
-	Sensitivity float64
-}
-
-type RuleTargetModeSelect struct {
-	RuleTargetBase
-	ModeSelect []string
-}