diff --git a/src/colspec.jl b/src/colspec.jl
index de9504c6..30ef15c7 100644
--- a/src/colspec.jl
+++ b/src/colspec.jl
@@ -10,7 +10,7 @@ const ColSelector = Union{Symbol,Integer,AbstractString}
 
 `ColSpec` is a union of types used to filter columns. 
 The `ColSpec` type together with the `ColSelector` union type and 
-the `_filter` internal function form the ColSpec interface.
+the `choose` function form the ColSpec interface.
 
 To implement the ColSpec interface, the following steps must be performed:
 
@@ -21,12 +21,12 @@ struct MyTransform{S<:ColSpec,#= other type params =#}
   # other fileds
 end
 ```
-2. use `_filter(colspec, names)` internal function in apply:
+2. use `choose(colspec, names)` function in apply:
 ```julia
 function apply(transform::MyTransform, table)
   names = Tables.columnnames(table)
   # selected column names
-  snames = _filter(transform.colspec, names)
+  snames = choose(transform.colspec, names)
   # code...
 end
 ```
@@ -41,33 +41,33 @@ end
 """
 const ColSpec = Union{Vector{T},NTuple{N,T},Regex,Colon} where {N,T<:ColSelector}
 
-# filter table columns using colspec
-function _filter(colspec::Vector{Symbol}, names)
+# choose column names using colspec
+function choose(colspec::Vector{Symbol}, names)
   # validate columns
   @assert !isempty(colspec) "Invalid column selection."
   @assert colspec ⊆ names "Invalid column selection."
   return colspec
 end
 
-_filter(colspec::Vector{<:AbstractString}, names) = 
-  _filter(Symbol.(colspec), names)
+choose(colspec::Vector{<:AbstractString}, names) = 
+  choose(Symbol.(colspec), names)
 
-_filter(colspec::Vector{<:Integer}, names::Vector) = 
-  _filter(names[colspec], names)
+choose(colspec::Vector{<:Integer}, names::Vector) = 
+  choose(names[colspec], names)
 
-_filter(colspec::Vector{<:Integer}, names::Tuple) = 
-  _filter(colspec, collect(names))
+choose(colspec::Vector{<:Integer}, names::Tuple) = 
+  choose(colspec, collect(names))
 
-_filter(colspec::NTuple{N,<:ColSelector}, names) where {N} =
-  _filter(collect(colspec), names)
+choose(colspec::NTuple{N,<:ColSelector}, names) where {N} =
+  choose(collect(colspec), names)
 
-function _filter(colspec::Regex, names::Vector)
-  fnames = filter(col -> occursin(colspec, String(col)), names)
-  _filter(fnames, names)
+function choose(colspec::Regex, names::Vector)
+  fnames = filter(n -> occursin(colspec, String(n)), names)
+  choose(fnames, names)
 end
 
-_filter(colspec::Regex, names::Tuple) = 
-  _filter(colspec, collect(names))
+choose(colspec::Regex, names::Tuple) = 
+  choose(colspec, collect(names))
 
-_filter(::Colon, names::Vector) = names
-_filter(::Colon, names::Tuple) = collect(names)
+choose(::Colon, names::Vector) = names
+choose(::Colon, names::Tuple) = collect(names)
diff --git a/src/transforms/filter.jl b/src/transforms/filter.jl
index daef0906..3c380eba 100644
--- a/src/transforms/filter.jl
+++ b/src/transforms/filter.jl
@@ -79,7 +79,7 @@ _nonmissing(x) = _nonmissing(eltype(x), x)
 function apply(transform::DropMissing, table)
   names = Tables.columnnames(table)
   types = Tables.schema(table).types
-  snames = _filter(transform.colspec, names)
+  snames = choose(transform.colspec, names)
   ftrans = _ftrans(transform, snames)
   newtable, fcache = apply(ftrans, table)
 
diff --git a/src/transforms/select.jl b/src/transforms/select.jl
index db389e51..5897a3b1 100644
--- a/src/transforms/select.jl
+++ b/src/transforms/select.jl
@@ -69,7 +69,7 @@ isrevertible(::Type{<:Select}) = true
 function apply(transform::Select, table)
   # retrieve relevant column names
   allcols = collect(Tables.columnnames(table))
-  select  = _filter(transform.colspec, allcols)
+  select  = choose(transform.colspec, allcols)
   reject  = setdiff(allcols, select)
 
   # keep track of indices to revert later
@@ -141,7 +141,7 @@ isrevertible(::Type{<:Reject}) = true
 
 function apply(transform::Reject, table)
   allcols = Tables.columnnames(table)
-  reject  = _filter(transform.colspec, allcols)
+  reject  = choose(transform.colspec, allcols)
   select  = setdiff(allcols, reject)
   strans  = Select(select)
   newtable, scache = apply(strans, table)
diff --git a/test/colspec.jl b/test/colspec.jl
new file mode 100644
index 00000000..1039ae17
--- /dev/null
+++ b/test/colspec.jl
@@ -0,0 +1,85 @@
+@testset "ColSpec" begin
+  vecnames = [:a, :b, :c, :d, :e, :f]
+  tupnames = (:a, :b, :c, :d, :e, :f)
+
+  # vector of symbols
+  colspec = [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, vecnames)
+  @test snames == [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, tupnames)
+  @test snames == [:a, :c, :e]
+
+  # tuple of symbols
+  colspec = (:a, :c, :e)
+  snames = TableTransforms.choose(colspec, vecnames)
+  @test snames == [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, tupnames)
+  @test snames == [:a, :c, :e]
+
+  # vector of strings
+  colspec = ["a", "c", "e"]
+  snames = TableTransforms.choose(colspec, vecnames)
+  @test snames == [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, tupnames)
+  @test snames == [:a, :c, :e]
+
+  # tuple of strings
+  colspec = ("a", "c", "e")
+  snames = TableTransforms.choose(colspec, vecnames)
+  @test snames == [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, tupnames)
+  @test snames == [:a, :c, :e]
+
+  # vector of integers
+  colspec = [1, 3, 5]
+  snames = TableTransforms.choose(colspec, vecnames)
+  @test snames == [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, tupnames)
+  @test snames == [:a, :c, :e]
+
+  # tuple of integers
+  colspec = (1, 3, 5)
+  snames = TableTransforms.choose(colspec, vecnames)
+  @test snames == [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, tupnames)
+  @test snames == [:a, :c, :e]
+
+  # regex
+  colspec = r"[ace]"
+  snames = TableTransforms.choose(colspec, vecnames)
+  @test snames == [:a, :c, :e]
+  snames = TableTransforms.choose(colspec, tupnames)
+  @test snames == [:a, :c, :e]
+
+  # colon
+  snames = TableTransforms.choose(:, vecnames)
+  @test snames == [:a, :b, :c, :d, :e, :f]
+  snames = TableTransforms.choose(:, tupnames)
+  @test snames == [:a, :b, :c, :d, :e, :f]
+
+  # throws
+  @test_throws AssertionError TableTransforms.choose(r"x", vecnames)
+  @test_throws AssertionError TableTransforms.choose(r"x", tupnames)
+  @test_throws AssertionError TableTransforms.choose(String[], vecnames)
+  @test_throws AssertionError TableTransforms.choose(String[], tupnames)
+  @test_throws AssertionError TableTransforms.choose(Symbol[], vecnames)
+  @test_throws AssertionError TableTransforms.choose(Symbol[], tupnames)
+
+  # type stability
+  @inferred TableTransforms.choose([:a, :b], vecnames)
+  @inferred TableTransforms.choose([:a, :b], tupnames)
+  @inferred TableTransforms.choose((:a, :b), vecnames)
+  @inferred TableTransforms.choose((:a, :b), tupnames)
+  @inferred TableTransforms.choose(["a", "b"], vecnames)
+  @inferred TableTransforms.choose(["a", "b"], tupnames)
+  @inferred TableTransforms.choose(("a", "b"), vecnames)
+  @inferred TableTransforms.choose(("a", "b"), tupnames)
+  @inferred TableTransforms.choose([1, 2], vecnames)
+  @inferred TableTransforms.choose([1, 2], tupnames)
+  @inferred TableTransforms.choose((1, 2), vecnames)
+  @inferred TableTransforms.choose((1, 2), tupnames)
+  @inferred TableTransforms.choose(r"[ab]", vecnames)
+  @inferred TableTransforms.choose(r"[ab]", tupnames)
+  @inferred TableTransforms.choose(:, vecnames)
+  @inferred TableTransforms.choose(:, tupnames)
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 48291b14..b744fe67 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -27,18 +27,18 @@ end
 Polynomial(args::T...) where {T<:Real} = Polynomial(collect(args))
 (p::Polynomial)(x) = sum(a * x^(i-1) for (i, a) in enumerate(p.coeffs))
 
-function isequalmissing(v1, v2)
-  length(v1) == length(v2) || return false
-  for (x, y) in zip(v1, v2)
+function isequalmissing(a, b)
+  length(a) == length(b) || return false
+  for (x, y) in zip(a, b)
     x === y || return false
   end
   return true
 end
 
-
 # list of tests
 testfiles = [
   "distributions.jl",
+  "colspec.jl",
   "transforms.jl"
 ]
 
diff --git a/test/transforms.jl b/test/transforms.jl
index 3497fee0..cacacf19 100644
--- a/test/transforms.jl
+++ b/test/transforms.jl
@@ -1,92 +1,6 @@
 @testset "Transforms" begin
   # using MersenneTwister for compatibility between Julia versions
   rng = MersenneTwister(42)
-  @testset "ColSpec" begin
-    veccols = [:a, :b, :c, :d, :e, :f]
-    tupcols = (:a, :b, :c, :d, :e, :f)
-    
-    # vector of symbols
-    colspec = [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, veccols)
-    @test cols == [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, tupcols)
-    @test cols == [:a, :c, :e]
-
-    # tuple of symbols
-    colspec = (:a, :c, :e)
-    cols = TableTransforms._filter(colspec, veccols)
-    @test cols == [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, tupcols)
-    @test cols == [:a, :c, :e]
-
-    # vector of strings
-    colspec = ["a", "c", "e"]
-    cols = TableTransforms._filter(colspec, veccols)
-    @test cols == [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, tupcols)
-    @test cols == [:a, :c, :e]
-
-    # tuple of strings
-    colspec = ("a", "c", "e")
-    cols = TableTransforms._filter(colspec, veccols)
-    @test cols == [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, tupcols)
-    @test cols == [:a, :c, :e]
-
-    # vector of integers
-    colspec = [1, 3, 5]
-    cols = TableTransforms._filter(colspec, veccols)
-    @test cols == [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, tupcols)
-    @test cols == [:a, :c, :e]
-
-    # tuple of integers
-    colspec = (1, 3, 5)
-    cols = TableTransforms._filter(colspec, veccols)
-    @test cols == [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, tupcols)
-    @test cols == [:a, :c, :e]
-
-    # regex
-    colspec = r"[ace]"
-    cols = TableTransforms._filter(colspec, veccols)
-    @test cols == [:a, :c, :e]
-    cols = TableTransforms._filter(colspec, tupcols)
-    @test cols == [:a, :c, :e]
-
-    # colon
-    cols = TableTransforms._filter(:, veccols)
-    @test cols == [:a, :b, :c, :d, :e, :f]
-    cols = TableTransforms._filter(:, tupcols)
-    @test cols == [:a, :b, :c, :d, :e, :f]
-
-    # throws
-    @test_throws AssertionError TableTransforms._filter(r"x", veccols)
-    @test_throws AssertionError TableTransforms._filter(r"x", tupcols)
-    @test_throws AssertionError TableTransforms._filter(String[], veccols)
-    @test_throws AssertionError TableTransforms._filter(String[], tupcols)
-    @test_throws AssertionError TableTransforms._filter(Symbol[], veccols)
-    @test_throws AssertionError TableTransforms._filter(Symbol[], tupcols)
-
-    # type stability
-    @inferred TableTransforms._filter([:a, :b], veccols)
-    @inferred TableTransforms._filter([:a, :b], tupcols)
-    @inferred TableTransforms._filter((:a, :b), veccols)
-    @inferred TableTransforms._filter((:a, :b), tupcols)
-    @inferred TableTransforms._filter(["a", "b"], veccols)
-    @inferred TableTransforms._filter(["a", "b"], tupcols)
-    @inferred TableTransforms._filter(("a", "b"), veccols)
-    @inferred TableTransforms._filter(("a", "b"), tupcols)
-    @inferred TableTransforms._filter([1, 2], veccols)
-    @inferred TableTransforms._filter([1, 2], tupcols)
-    @inferred TableTransforms._filter((1, 2), veccols)
-    @inferred TableTransforms._filter((1, 2), tupcols)
-    @inferred TableTransforms._filter(r"[ab]", veccols)
-    @inferred TableTransforms._filter(r"[ab]", tupcols)
-    @inferred TableTransforms._filter(:, veccols)
-    @inferred TableTransforms._filter(:, tupcols)
-  end
-
   @testset "Select" begin
     a = rand(4000)
     b = rand(4000)