Add tests to ci

Test pyflix and simulation using pytest.
Fix running the sim in non-tty environment.
Test presence of some essential files in the docs.

tools/requirements.txt

@@ -1,3 +1,4 @@
+pymavlink
 docopt
 matplotlib
 mcap

tools/test.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+
+# Script for testing pyflix and the simulation.
+
+from pytest import approx
+from math import isnan, isfinite
+import time
+from pyflix import Flix
+
+def test():
+    print('=== Connect...')
+    flix = Flix(timeout=20)
+
+    print('=== Check initial state')
+    time.sleep(1)  # give more time for initial state
+    assert flix.connected
+    assert flix.mode == 'STAB'
+    assert not flix.armed
+    assert flix.landed
+    assert isnan(flix.voltage) or flix.voltage == approx(4.2)
+    assert flix.rates == approx((0, 0, 0), abs=0.01)
+    assert flix.attitude == approx((1, 0, 0, 0), abs=0.01)
+    assert flix.attitude_euler == approx((0, 0, 0), abs=0.01)
+    assert all(m == 0 for m in flix.motors)
+    assert flix.acc == approx((0, 0, 9.81), abs=0.1)
+    assert flix.gyro == approx((0, 0, 0), abs=0.01)
+    assert all(ch == 0 for ch in flix.channels)
+
+    print('=== Check console commands')
+    assert 'Time: ' in flix.cli('time')
+    assert 'landed: 1' in flix.cli('imu')
+
+    print('=== Check parameters')
+    assert isfinite(flix.get_param('CTL_ATT_P_P'))
+    flix.set_param('CTL_ATT_P_P', 10.0)
+
+    print('=== Additional checks')
+    assert flix.wait('gyro') == approx((0, 0, 0), abs=0.01)
+    flix.wait('armed', False)
+    flix.wait('mode', 'STAB')
+    flix.wait('motors', lambda motors: not any(motors))
+    flix.set_armed(True)
+    flix.wait('armed', True)
+    flix.set_mode('ACRO')
+    flix.wait('mode', 'ACRO')
+    flix.set_mode('AUTO')
+    flix.wait('mode', 'AUTO')