Fixes for SimpleCrop unit tests

src/crop/simplecrop.jl

@@ -12,7 +12,9 @@ import Persefone:
     cropname,
     cropheight,
     cropcover,
-    cropyield
+    cropyield,
+    sow!,
+    harvest!
 
 struct CropType
     name::String
@@ -50,7 +52,7 @@ Change the cropstate to sow the specified crop.
 """
 function sow!(cs::CropState, model::SimulationModel, cropname::String)
     cs.croptype = model.crops[cropname]
-    cs.height = 0cm
+    cs.height = 0.0cm
 end
 
 """