Add tests

Author: hersle

test/variable_parsing.jl

@@ -104,13 +104,15 @@ end
     y = 2, [connect = Flow]
 end
 
+@test_throws ErrorException ModelingToolkit.getdefault(x)
 @test !hasmetadata(x, VariableDefaultValue)
 @test getmetadata(x, VariableConnectType) == Flow
 @test getmetadata(x, VariableUnit) == u
 @test getmetadata(y, VariableDefaultValue) === 2
 @test getmetadata(y, VariableConnectType) == Flow
 
 a = rename(value(x), :a)
+@test_throws ErrorException ModelingToolkit.getdefault(x)
 @test !hasmetadata(x, VariableDefaultValue)
 @test getmetadata(x, VariableConnectType) == Flow
 @test getmetadata(x, VariableUnit) == u