finished interpreter. still need to test it

package/test/InterpreterTests.jl

@@ -41,6 +41,23 @@ end
 	@test isequal(result, reference)
 end
 
+@testset "Test Add Operator" begin
+	# One test with fixed values
+	# One test with variables
+	# One test with parameters
+end
+@testset "Test Subtract Operator" begin
+	# One test with fixed values
+	# One Test with fixed values but swapped
+	# One test with variables
+	# One test with parameters
+end
+@testset "Test Abs Operator" begin
+	# One test with fixed value
+	# One test with variable
+	# One test with parameter
+end
+
 # TODO: Add several tests fo the mathematical expressions
 #       One test for each operator. A second test if the operation order matters
 #       And some more complicated expressions, with some only having variables, some only having parameters and some having both