dPID: Exercise

status:

pre-alpha

TDD-approach

Test first

First, write some test-files with test-functions that verify the correct working of the dpid.dPID class as specified. Depending on your knowledge of PID-controllers these test may (functionally) vary. The primary goal here is not to program (including testing) a great PID-controller; but to practice your python-skills.

Hint

time-dependent

The dpid.dPID class is discrete; it only calculates the dpid.dPID.result() when requested. This implies the (return) value of dpid.dPID.result() will depend on when it is called (relative to the other methods).

• So, timing may be relavant in your (test)-code. One can use time.sleep to controll that. Usa a floating-point parameter for sub-second resolution. Typically, the function is accurate in the milli-seconds range.

• Compare using a small MARGIN, to allow derivations due e.g. timing. See the examples.

See also

Convenient python functions

• https://docs.python.org/3.5/library/time.html?highlight=sleep#time.sleep

• https://docs.python.org/3.5/library/functions.html?highlight=abs#abs

Instructions

• Use the pytest framework, to shorten test-code.

  • Pytest introduction is a summary with everything you need for this exercise.

  • You can use Some (py)test examples as template for your own files.

• Start by running pytest as shown.

  • Reproduce the shown output first, before adding your own files.

  • Remember; the output text will differ slightly; for paths, dates etc.

• Add a (one) new file: test_<something>.py.

  • Copy the start of the file (above the first function); update the copyright.

  • Write a single test-function:

    • Create a dpid.dPID instance with known, simple P, I and D settings.

    • Give it a setpoint() and measured() value.

    • Request a result().

    • Assert the returned value is (almost) equal to the pre-computed number.

• Run pytest again.

  • It should run both the existing example, and the new test-file.

  • The test should fail! As the empty class always returns 0, that is easy.

  • Watch for syntax and other errors! All, but AssertionError, should be resolved in your code

• Repeat, either by adding a test-function to that file, or adding more test-files.

  • When needed, you can add auxiliary functions; just don’t use the test-phrase in its name.

  • Or continue first with the implementation part. And add more test later (for other functions).

  • Each test should be a little more complicated as the existing onces.

  • Or better: start with the trivial once. Then the almost-trivial, etc.

    • Start testing a “P-only” PID-controller

    • Then an “I-only”, then a “D-only”. After which you test a simple combination

    • etc.

Code second

When a part of the functionality is tested (or at least: there is test-code for), you can start implementing the dPID class. Keep is simple. The only objective is to make one failing test pass.

And improve (refactor)

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