InstrumentMock.Core 0.2.0

InstrumentMock

Lightweight SCPI and Modbus TCP device simulator for integration testing.

Spin up a realistic instrument mock in one line of C# code.
No Docker. No admin rights. No hardware required. Runs on any Windows CI agent.

Quick Start

// Load device model from YAML and start SCPI server on port 5025
await using var device = MockDevice.FromYaml("devices/generic_psu.yaml", port: 5025);
await device.StartAsync();

// Your test code connects via TCP to localhost:5025
// Any VISA-compatible client works: pyvisa, python-ivi, NI-VISA, ...

await device.StopAsync();

In a test (xUnit example)

[Fact]
public async Task PowerSupply_SetsVoltage()
{
    await using var device = MockDevice.FromYaml("generic_psu.yaml", port: 5025);
    await device.StartAsync();

    // Connect your real driver under test to localhost:5025
    var psu = new MyPsuDriver("localhost", 5025);
    await psu.SetVoltageAsync(12.5);

    Assert.Equal("12.5", device.StateMachine.GetState("voltage_set"));
}

Device Model (YAML)

Each device is described by a simple YAML file:

id: my_psu
name: My Power Supply
manufacturer: Keysight
model: E36312A
firmware: A.01.07
serial: MY12345678

initial_state:
  voltage_set: "0.0"
  current_set: "1.0"
  output_enabled: "0"

commands:
  - pattern: "VOLT {value}"
    description: "Set output voltage"
    min: 0.0
    max: 32.0
    set_state:
      voltage_set: "{value}"

  - pattern: "VOLT?"
    response: "{voltage_set}"

  - pattern: "OUTP {state}"
    set_state:
      output_enabled: "{state}"

  - pattern: "OUTP?"
    response: "{output_enabled}"

  - pattern: "MEAS:VOLT?"
    response: "{voltage_set}"

Built-in IEEE 488.2 commands (always available)

Architecture

DeviceModel (YAML)
      │
      ▼
DeviceStateMachine   ←── stateful, thread-safe
      │
      ▼
ScpiServer (TCP :5025)
      │
      ▼
Your test code / driver under test

Modbus TCP

await using var device = MockModbusDevice.FromYaml("devices/relay_board.yaml", port: 502);
await device.StartAsync();

// Inject a measured value from the "sensor" side
device.Registers.SetInput(0, 2450); // e.g. 24.50 V (10mV resolution)

// Assert what the client wrote
var setpoint = device.Registers.GetHolding(0);

Supported function codes: FC01–FC06, FC0F, FC10 (coils, discrete inputs, holding/input registers).

Roadmap

• SCPI/TCP support
• Modbus/TCP support (relay boards, EA PSUs)
• Fault injection API (response delay, error queue, drop/override)
• KI-based YAML generation from instrument manuals (paid service)
• Device library (verified YAML files for common instruments)
• Serial port (RS232) transport

License

MIT – Core library is free and open source forever.
Premium device models available at [instrumentmock (coming soon) (coming soon)