libfprint/tests

umockdev Tests

umockdev tests use fingerprint devices mocked by umockdev toolchain.

This document describes how to create a 'capture' test: a test that captures a picture of a fingerprint from the device (mocked by umockdev) and compares it with the standard one.

Other kinds of umockdev tests could be created in a similar manner.

'Capture' Test Creation

A new 'capture' test is created by means of capture.py script:

1. Create (if needed) a directory for the driver under tests directory:

   mkdir DRIVER

2. Prepare your execution environment.

   In the next step a working and up to date libfprint is needed. This can be achieved by installing it into your system. Alternatively, you can set the following environment variables to run a local build:

   • export LD_PRELOAD=<meson-build-dir>/libfprint/libfprint-2.so
   • export GI_TYPELIB_PATH=<meson-build-dir>/libfprint

   Also, sometimes the driver must be adopted to the emulated environment (mainly if it uses random numbers, see synaptics.c for an example). Set the following environment variable to enable this adaptation:

   • export FP_DEVICE_EMULATION=1

   Run the next steps in the same terminal.

3. Find the real USB fingerprint device with lsusb, e.g.:

   Bus 001 Device 005: ID 138a:0090 Validity Sensors, Inc. VFS7500 Touch Fingerprint Sensor

   The following USB device is used in the example above: /dev/bus/usb/001/005.

4. Record information about this device:

   umockdev-record /dev/bus/usb/001/005 > DRIVER/device

5. Record interaction of capture.py (or other test) with the device:

   umockdev-record -i /dev/bus/usb/001/005=DRIVER/capture.ioctl -- python3 ./capture.py DRIVER/capture.png

   Files capture.ioctl and capture.png will be created as the result of this command.

6. Add driver's name to drivers_tests in the meson.build.

7. Check whether everything works as expected.

Note. To avoid submitting a real fingerprint, the side of finger, arm, or anything else producing an image with the device can be used.

Possible Issues

umockdev-record aggressively groups URBs. In most cases, manual intervention is unfortunately required. Often, drivers do a chain of commands like: A then B each with a different reply. However, umockdev-record could create a file like this:

A
 reply 1
 reply 2
B
 reply 1
 reply 2

In that case, records must be re-ordered:

A
 reply 1
B
 reply 1
A
 reply 2
B
 reply 2

Other changes may be needed to get everything working. For example the elan driver relies on a timeout that is not reported correctly. In this case the driver works around it by interpreting the protocol error differently in the virtual environment (by means of FP_DEVICE_EMULATION environment variable).