Fix averagefieldsize and simplify code

- When there are no fields `averagefieldsize` would return a unitless
  number.  This is now fixed.

- An unnecessary allocation was removed

- Fix unit tests, use approximate floating point comparison

src/crop/farmplot.jl

@@ -96,11 +96,9 @@ end
 Calculate the average field size in hectares for the model landscape.
 """
 function averagefieldsize(model::SimulationModel)
-    sizes::Vector{Float64} = []
-    for fp in model.farmplots
-        push!(sizes, @areaof(length(fp.pixels)))
-    end
-    return sum(sizes)/length(sizes) |> ha
+    area_sum = sum(@areaof(length(fp.pixels)) for fp in model.farmplots; init=0.0u"m^2")
+    area_avg = area_sum / length(model.farmplots)
+    return area_avg |> ha
 end
 
 """

test/landscape_tests.jl

@@ -14,7 +14,7 @@
     @test Ps.landcover((400,400), model) == Ps.grass
     @test Ps.landcover((800,800), model) == Ps.agriculture
     @test Ps.landcover((1100,1100), model) == Ps.builtup
-    @test Ps.averagefieldsize(model) == 5.37
+    @test isapprox(Ps.averagefieldsize(model), 5.374u"ha"; atol=1e-3u"ha")
     @test count(f -> ismissing(f.fieldid), model.landscape) == 1685573
     @test length(Ps.farmplot((800,800), model).pixels) == 4049               
 end

test/runtests.jl

@@ -20,7 +20,7 @@ const Ps = Persefone
 const TESTPARAMETERS = joinpath(pkgdir(Persefone), "test/test_parameters.toml")
 const TESTSETTINGS = Ps.getsettings(TESTPARAMETERS)
 
-import Unitful: cm, m, km, ha, mg, g, kg, Length, Area, Mass
+import Unitful: @u_str, cm, m, km, ha, mg, g, kg, Length, Area, Mass
 const m² = m^2
 const km² = km^2