the group names of a dataset without groups should be [] for consistency

Author: Alexander-Barth

src/dataset.jl

@@ -33,7 +33,7 @@ sync(ds::AbstractDataset) = nothing
 All the subgroup names of the data set `ds`. For a data set containing
 only a single group, this will be an empty vector of `String`.
 """
-groupnames(ds::AbstractDataset) = ()
+groupnames(ds::AbstractDataset) = []
 
 
 """

test/test_empty.jl

@@ -5,21 +5,21 @@ end
 
 
 dd = DummyEmptyDataset();
-@test CDM.dimnames(dd) == ()
+@test length(CDM.dimnames(dd)) == 0
 @test_throws Exception CDM.dim(dd,"does_not_exist")
 @test_throws Exception CDM.defDim(dd,"does_not_exist",1)
 
-@test CDM.attribnames(dd) == ()
+@test length(CDM.attribnames(dd)) == 0
 @test_throws Exception CDM.attrib(dd,"does_not_exist")
 @test_throws Exception CDM.defAttrib(dd,"does_not_exist",1)
 
-@test CDM.varnames(dd) == ()
+@test length(CDM.varnames(dd)) == 0
 @test_throws Exception CDM.variable(dd,"does_not_exist")
 @test_throws Exception CDM.defVar(dd,"does_not_exist",Int32,())
 
 @test CDM.path(dd) == ""
 
-@test CDM.groupnames(dd) == ()
+@test length(CDM.groupnames(dd)) == 0
 # not available in julia 1.6
 #@test_throws "no group" CDM.group(dd,"does_not_exist")
 #@test_throws "unimplemented" CDM.defGroup(dd,"does_not_exist")