Added several tests

tests/test_pid.py

@@ -13,23 +13,137 @@ def test_P():
     pid = PID(1, 0, 0, setpoint=10, sample_time=None)
     assert pid(0) == 10
     assert pid(5) == 5
+    assert pid(-5) == 15
+
+
+def test_P_negative_setpoint():
+    pid = PID(1, 0, 0, setpoint=-10, sample_time=None)
+    assert pid(0) == -10
+    assert pid(5) == -15
+    assert pid(-5) == -5
+    assert pid(-15) == 5
+
+
+def test_I():
+    pid = PID(0, 10, 0, setpoint=10, sample_time=0.1)
+    time.sleep(0.1)
+
+    assert round(pid(0)) == 10.0  # make sure we are close to expected value
+    time.sleep(0.1)
 
+    assert round(pid(0)) == 20.0
+
+
+def test_I_negative_setpoint():
+    pid = PID(0, 10, 0, setpoint=-10, sample_time=0.1)
+    time.sleep(0.1)
+
+    assert round(pid(0)) == -10.0
+    time.sleep(0.1)
+
+    assert round(pid(0)) == -20.0
+
+
+def test_D():
+    pid = PID(0, 0, 1, setpoint=10, sample_time=None)
+
+    # should not compute derivate when there is no previous input (don't assume 0 as first input)
+    assert pid(0) == 0
+
+    # derivate is 0 when input is the same
+    assert pid(0) == 0
+    assert pid(0) == 0
+
+    assert pid(5) == -5
+    assert pid(20) == -15
+
+
+def test_D_negative_setpoint():
+    pid = PID(0, 0, 1, setpoint=-10, sample_time=None)
+
+    # should not compute derivate when there is no previous input (don't assume 0 as first input)
+    assert pid(0) == 0
+
+    # derivate is 0 when input is the same
+    assert pid(0) == 0
+    assert pid(0) == 0
+
+    assert pid(5) == -5
+    assert pid(-5) == 10
+    assert pid(-30) == 25
+
+
+def test_desired_state():
+    pid = PID(10, 5, 2, setpoint=10, sample_time=None)
+
+    # should not make any adjustment when setpoint is achieved
+    assert pid(10) == 0
+
+
+def test_output_limits():
+    pid = PID(100, 20, 40, setpoint=10, output_limits=(0, 100), sample_time=None)
+    time.sleep(0.1)
+
+    assert 0 <= pid(0) <= 100
+    time.sleep(0.1)
+
+    assert 0 <= pid(-100) <= 100
+
+
+def test_sample_time():
+    pid = PID(setpoint=10, sample_time=10)
+
+    control = pid(0)
+
+    # last value should be returned again
+    assert pid(100) == control
+
+
+def test_clamp():
+    from simple_pid.PID import _clamp
+
+    assert _clamp(None, (None, None)) == None
+    assert _clamp(None, (-10, 10)) == None
+
+    # no limits
+    assert _clamp(0, (None, None)) == 0
+    assert _clamp(100, (None, None)) == 100
+    assert _clamp(-100, (None, None)) == -100
+
+    # only lower limit
+    assert _clamp(0, (0, None)) == 0
+    assert _clamp(100, (0, None)) == 100
+    assert _clamp(-100, (0, None)) == 0
+
+    # only upper limit
+    assert _clamp(0, (None, 0)) == 0
+    assert _clamp(100, (None, 0)) == 0
+    assert _clamp(-100, (None, 0)) == -100
+
+    # both limits
+    assert _clamp(0, (-10, 10)) == 0
+    assert _clamp(-10, (-10, 10)) == -10
+    assert _clamp(10, (-10, 10)) == 10
+    assert _clamp(-100, (-10, 10)) == -10
+    assert _clamp(100, (-10, 10)) == 10
+
 
-def test_control():
-    pid = PID(2, 1, 1, setpoint=10)
-    PV = 0
+def test_converge_system():
+    pid = PID(1, 0.8, 4, setpoint=5, output_limits=(-5, 5))
+    PV = 0  # process variable
 
     def update_system(C, dt):
+        # calculate a simple system model
         return PV + C*dt - 1*dt
 
     start_time = time.time()
     last_time = start_time
 
-    while time.time() - start_time < 10:
+    while time.time() - start_time < 120:
         C = pid(PV)
         PV = update_system(C, time.time()-last_time)
 
         last_time = time.time()
 
     # check if system has converged
-    assert abs(PV - 10) < 0.1
+    assert abs(PV - 5) < 0.1

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27, py36, pypy
+envlist = py2, py3
 
 [testenv]
 commands = pytest