put in test for #31 and fix here

other places (e.g. widgets) should accept missing gradient and render something sensible

gopro_overlay/timeseries_process.py

@@ -64,10 +64,11 @@ def calculate_gradient():
     # have to move a bit (0.10m) to calculate decent gradient
     # this is called for frames ~2 sec apart.
     def accept(a, b, c):
-        gain = b.alt - a.alt
-        if a.odo and b.odo:
-            dist = b.odo - a.odo
-            if dist and dist.magnitude > 0.10:
-                return {"grad": (gain / dist) * 100.0}
+        if a.alt and b.alt:
+            gain = b.alt - a.alt
+            if a.odo and b.odo:
+                dist = b.odo - a.odo
+                if dist and dist.magnitude > 0.10:
+                    return {"grad": (gain / dist) * 100.0}
 
     return accept

tests/test_timeseries.py

@@ -3,7 +3,7 @@
 from gopro_overlay.entry import Entry
 from gopro_overlay.point import Point
 from gopro_overlay.timeseries import Timeseries
-from gopro_overlay.timeseries_process import process_ses, calculate_speeds
+from gopro_overlay.timeseries_process import process_ses, calculate_speeds, calculate_gradient
 from gopro_overlay.units import units
 
 
@@ -56,3 +56,26 @@ def test_process_delta_speeds():
     assert "{0.magnitude:.2f} {0.units:~P}".format(entry.cspeed) == "16.11 m/s"
     assert "{0.magnitude:.2f} {0.units:~P}".format(entry.azi) == "56.53 deg"
     assert "{0.magnitude:.2f} {0.units:~P}".format(entry.cog) == "56.53 deg"
+
+
+def metres(n):
+    return units.Quantity(n, units.m)
+
+
+def test_process_gradient():
+    processor = calculate_gradient()
+    r = processor(
+        a=Entry(datetime_of(0), alt=metres(5), odo=metres(10)),
+        b=Entry(datetime_of(0), alt=metres(6), odo=metres(26)),
+        c=None
+    )
+    assert r["grad"].magnitude == 6.25
+
+
+def test_process_gradient_missing_alt():
+    processor = calculate_gradient()
+    assert processor(
+        a=Entry(datetime_of(0), odo=metres(10)),
+        b=Entry(datetime_of(0), alt=metres(6), odo=metres(26)),
+        c=None
+    ) is None