Added the files for the test suite

test/crop_tests.jl

+### Persephone - a socio-economic-ecological model of European agricultural landscapes.
+###
+### These are the tests for the crop growth model.
+###
+
+#TODO

test/farm_tests.jl

+### Persephone - a socio-economic-ecological model of European agricultural landscapes.
+###
+### These are the tests for the farm model.
+###
+
+#TODO

test/landscape_tests.jl

+### Persephone - a socio-economic-ecological model of European agricultural landscapes.
+###
+### These are the tests for the core landscape functions.
+###
+
+#TODO

test/nature_tests.jl

+### Persephone - a socio-economic-ecological model of European agricultural landscapes.
+###
+### These are the tests for the nature model (excluding individual species).
+###
+
+#TODO

test/runtests.jl

+### Persephone - a socio-economic-ecological model of European agricultural landscapes.
+###
+### This is the top-level file of the Persephone test suite. Execute this to run all tests.
+###
+
+using Pkg
+Pkg.activate("..")
+
+using Persephone
+using Test
+
+@testset "Persephone Tests" begin
+    @testset "Core model" begin
+        include("landscape_tests.jl")
+        include("simulation_tests.jl")
+    end
+    @testset "Nature model" begin
+        include("nature_tests.jl")
+    end
+    @testset "Crop growth model" begin
+        include("crop_tests.jl")
+    end
+    @testset "Farm model" begin
+        include("farm_tests.jl")
+    end
+end

test/simulation_tests.jl

+### Persephone - a socio-economic-ecological model of European agricultural landscapes.
+###
+### These are the tests for the core simulation functions.
+###
+
+#TODO