diff --git a/internal/tester/driver.go b/internal/tester/driver.go
new file mode 100644
index 0000000..4859da9
--- /dev/null
+++ b/internal/tester/driver.go
@@ -0,0 +1,59 @@
+package tester
+
+import (
+	"errors"
+	"time"
+)
+
+// ErrNotConnected is returned by Read() when Connect() has not been called.
+var ErrNotConnected = errors.New("tester: not connected — call Connect() first")
+
+// CableType identifies the physical cable standard being tested.
+type CableType int
+
+const (
+	CableTypeUSB  CableType = iota
+	CableTypeDP
+	CableTypeHDMI
+)
+
+// TestResult captures all measurements from a single cable test run.
+type TestResult struct {
+	CableType     CableType
+	USBVersion    string
+	DPVersion     string
+	HDMIVersion   string
+	SpeedGbps     float64
+	MaxWatts      int
+	PinContinuity bool
+	HasEMarker    bool
+	ResistanceOhm float64
+}
+
+// LiveReading is a single sample from a streaming power/protocol meter (e.g. FNB58).
+type LiveReading struct {
+	Voltage     float64
+	CurrentAmps float64
+	PowerWatts  float64
+	PDProtocol  string
+	Timestamp   time.Time
+}
+
+// TesterDriver is the common interface for all discrete cable testers.
+// Connect must be called before Read.
+// Disconnect is idempotent.
+type TesterDriver interface {
+	Connect() error
+	Read() (TestResult, error)
+	Disconnect() error
+}
+
+// StreamingTesterDriver extends TesterDriver for devices that continuously
+// emit live power/protocol readings (e.g. FNIRSI FNB58).
+// Stream() returns a read-only channel that emits LiveReading values and is
+// closed when the stream ends or Disconnect() is called.
+// Calling Stream() before Connect() returns a pre-closed channel.
+type StreamingTesterDriver interface {
+	TesterDriver
+	Stream() <-chan LiveReading
+}
diff --git a/internal/tester/mock_drivers.go b/internal/tester/mock_drivers.go
new file mode 100644
index 0000000..3a2079b
--- /dev/null
+++ b/internal/tester/mock_drivers.go
@@ -0,0 +1,175 @@
+package tester
+
+import (
+	"context"
+	"time"
+)
+
+// MockUSBDriver simulates a Treedix USB cable tester.
+// Returns deterministic USB 3.2 Gen 2 test results.
+// All fields are exported so test code can construct zero values directly.
+type MockUSBDriver struct {
+	connected bool
+}
+
+// Compile-time interface assertion.
+var _ TesterDriver = (*MockUSBDriver)(nil)
+
+func (d *MockUSBDriver) Connect() error {
+	d.connected = true
+	return nil
+}
+
+func (d *MockUSBDriver) Read() (TestResult, error) {
+	if !d.connected {
+		return TestResult{}, ErrNotConnected
+	}
+	return TestResult{
+		CableType:     CableTypeUSB,
+		USBVersion:    "USB 3.2 Gen 2",
+		SpeedGbps:     10.0,
+		MaxWatts:      100,
+		PinContinuity: true,
+		HasEMarker:    true,
+		ResistanceOhm: 0.12,
+	}, nil
+}
+
+func (d *MockUSBDriver) Disconnect() error {
+	d.connected = false
+	return nil
+}
+
+// MockDPDriver simulates a Treedix DisplayPort cable tester.
+// Returns deterministic DP 1.4 test results.
+type MockDPDriver struct {
+	connected bool
+}
+
+// Compile-time interface assertion.
+var _ TesterDriver = (*MockDPDriver)(nil)
+
+func (d *MockDPDriver) Connect() error {
+	d.connected = true
+	return nil
+}
+
+func (d *MockDPDriver) Read() (TestResult, error) {
+	if !d.connected {
+		return TestResult{}, ErrNotConnected
+	}
+	return TestResult{
+		CableType:     CableTypeDP,
+		DPVersion:     "1.4",
+		PinContinuity: true,
+	}, nil
+}
+
+func (d *MockDPDriver) Disconnect() error {
+	d.connected = false
+	return nil
+}
+
+// MockHDMIDriver simulates a Treedix HDMI cable tester.
+// Returns deterministic HDMI 2.1 test results.
+type MockHDMIDriver struct {
+	connected bool
+}
+
+// Compile-time interface assertion.
+var _ TesterDriver = (*MockHDMIDriver)(nil)
+
+func (d *MockHDMIDriver) Connect() error {
+	d.connected = true
+	return nil
+}
+
+func (d *MockHDMIDriver) Read() (TestResult, error) {
+	if !d.connected {
+		return TestResult{}, ErrNotConnected
+	}
+	return TestResult{
+		CableType:     CableTypeHDMI,
+		HDMIVersion:   "2.1",
+		PinContinuity: true,
+	}, nil
+}
+
+func (d *MockHDMIDriver) Disconnect() error {
+	d.connected = false
+	return nil
+}
+
+// MockFNB58Driver simulates an FNIRSI FNB58 USB power meter.
+// Stream() emits 3 deterministic LiveReading samples at 100ms intervals,
+// then closes the channel. Disconnect() cancels the goroutine early.
+type MockFNB58Driver struct {
+	connected  bool
+	streamCh   chan LiveReading
+	cancelFunc context.CancelFunc
+}
+
+// Compile-time interface assertion.
+var _ StreamingTesterDriver = (*MockFNB58Driver)(nil)
+
+func (d *MockFNB58Driver) Connect() error {
+	d.connected = true
+	d.streamCh = make(chan LiveReading, 8)
+	ctx, cancel := context.WithCancel(context.Background())
+	d.cancelFunc = cancel
+	go d.runStream(ctx)
+	return nil
+}
+
+func (d *MockFNB58Driver) runStream(ctx context.Context) {
+	defer close(d.streamCh)
+	samples := []LiveReading{
+		{Voltage: 5.1, CurrentAmps: 3.0, PowerWatts: 15.3, PDProtocol: "PD3.0", Timestamp: time.Now()},
+		{Voltage: 5.1, CurrentAmps: 3.0, PowerWatts: 15.3, PDProtocol: "PD3.0", Timestamp: time.Now()},
+		{Voltage: 5.1, CurrentAmps: 3.0, PowerWatts: 15.3, PDProtocol: "PD3.0", Timestamp: time.Now()},
+	}
+	for _, s := range samples {
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(100 * time.Millisecond):
+			s.Timestamp = time.Now()
+			select {
+			case d.streamCh <- s:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}
+}
+
+func (d *MockFNB58Driver) Read() (TestResult, error) {
+	if !d.connected {
+		return TestResult{}, ErrNotConnected
+	}
+	// FNB58 is a streaming device; discrete Read returns a snapshot.
+	return TestResult{
+		CableType: CableTypeUSB,
+		MaxWatts:  100,
+	}, nil
+}
+
+func (d *MockFNB58Driver) Disconnect() error {
+	if d.cancelFunc != nil {
+		d.cancelFunc()
+		d.cancelFunc = nil
+	}
+	d.connected = false
+	return nil
+}
+
+// Stream returns the live reading channel. If called before Connect(),
+// returns a pre-closed channel (never nil, never blocking).
+func (d *MockFNB58Driver) Stream() <-chan LiveReading {
+	if !d.connected || d.streamCh == nil {
+		closed := make(chan LiveReading)
+		close(closed)
+		return closed
+	}
+	return d.streamCh
+}
diff --git a/internal/usb/device.go b/internal/usb/device.go
index 4520682..2fc2ea7 100644
--- a/internal/usb/device.go
+++ b/internal/usb/device.go
@@ -33,7 +33,12 @@ func (s DeviceSpec) String() string { return s.VIDPID() + " (" + s.Name + ")" }
 // Update VID/PID values after hardware characterization on 2026-04-13.
 var KnownDevices = map[string]DeviceSpec{
 	"0525:a4a7": {VID: "0525", PID: "a4a7", Name: "PRT Qutie", Role: RolePrinter, BaudRate: 9600},
-	// Phase 5: Treedix testers will be added here after characterization
+	// TODO(hardware): Replace placeholder VID:PIDs after characterization 2026-04-13
+	"dead0:0001": {VID: "dead0", PID: "0001", Name: "Treedix USB Tester", Role: RoleCableTester, BaudRate: 115200},
+	"dead0:0002": {VID: "dead0", PID: "0002", Name: "Treedix DP Tester", Role: RoleCableTester, BaudRate: 115200},
+	"dead0:0003": {VID: "dead0", PID: "0003", Name: "Treedix HDMI Tester", Role: RoleCableTester, BaudRate: 115200},
+	// TODO(hardware): BaudRate 0 = HID protocol — replace VID:PID after characterization
+	"dead0:0004": {VID: "dead0", PID: "0004", Name: "FNIRSI FNB58", Role: RoleCableTester, BaudRate: 0},
 }
 
 // DeviceState represents the current connection status of a managed device.