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Learn an efficient way to mock a `UART` serial port connection in Linux using socat for automated testing, ensuring your code stays robust against future changes.
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How to Mock a UART Serial Port in Linux for Efficient Testing

In the world of embedded programming and automation, the ability to mock serial communication can save you countless hours of troubleshooting and manual testing. A common scenario arises when working with microcontrollers and Linux systems, specifically when you need to simulate a serial connection for purposes such as testing. This post dives into how you can effectively mock a UART serial port in Linux, particularly using the socat tool.

The Problem at Hand

Imagine you're developing a project involving a microcontroller—perhaps an Arduino—reading data from a CAN bus and then sending it over a UART serial connection to a BananaPi Zero M2 running Arch Linux. The challenge comes from the constant changes in your project, which compel you to frequently compile and test your code. Ideally, you want a way to emulate this serial connection, eliminating unnecessary compilation time while ensuring that messages are being transmitted correctly.

You might have already tried various options to mock this connection. In this guide, we will cover a straightforward solution using socat, allowing you to create virtual serial devices and streamline your testing process.

Using socat to Create Virtual Serial Ports

What is socat?

socat (SOcket CAT) is a command-line based utility that establishes two bidirectional byte streams and transfers data between them. It can be used to mock serial connections effectively.

Setting Up socat

To emulate the serial connection using socat, you essentially create two pseudo terminals (pty) that allow data transfer between them. Here’s a simplified breakdown of how to do this:

Install socat: If you don't have socat installed on your Linux system, you can typically find it in your package manager. For Arch Linux, you would use:

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Run socat: You can create two virtual devices that will communicate with each other. The command you would run in your terminal resembles:

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This command creates two pty devices, /tmp/banana and /tmp/tango, that can be used as serial ports.

Example Implementation

Here's how you can utilize the mocked serial connection in your C+ + code with Qt:

Setting Up the Test

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Sending a Message

Here’s how you can send a message and verify it:

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Handling the ReadyRead Signal

One crucial aspect often overlooked is handling the readyRead() signal correctly.

The Issue

Initially, you might notice that the readyRead signal does not trigger as expected. This happens because the signal has a delay and does not synchronize with other operations seamlessly.

The Solution

To ensure you’re processing the incoming data correctly, use the waitForReadyRead() method:

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This implementation will block until data is available for reading, without freezing your process, allowing your tests to accurately reflect the serial communication state.

Conclusion

Mocking a UART serial port in Linux can significantly enhance your testing capabilities, providing a controlled environment to verify data transmission without the constant need for hardware connections. Using socat to create virtual serial ports alongside proper handling in your application ensures your tests are both robust and efficient.

By following this guide, you can create a flexible testing setup for your embedded development project that adapts well to frequent changes and testing needs. Happy coding!