add groupby() test from JuliaData#862

Author: alyst

test/grouping.jl

@@ -29,4 +29,8 @@ module TestGrouping
     h(df) = g(f(df))
 
     @test combine(map(h, gd)) == combine(map(g, ga))
+
+    df2 = DataFrame(v1 = pool(collect(1:1000)), v2 = pool(fill(1, 1000)))
+    @test groupby(df2, [:v1, :v2]).starts == collect(1:1000)
+    @test groupby(df2, [:v2, :v1]).starts == collect(1:1000)
 end