[DF] Add test for HasColumn and change test file name

tree/dataframe/test/CMakeLists.txt

@@ -2,7 +2,7 @@
 
 #### C++ TESTS ####
 ROOT_ADD_GTEST(dataframe_friends dataframe_friends.cxx LIBRARIES ROOTDataFrame)
-ROOT_ADD_GTEST(dataframe_alias dataframe_aliases.cxx LIBRARIES ROOTDataFrame)
+ROOT_ADD_GTEST(dataframe_colnames dataframe_colnames.cxx LIBRARIES ROOTDataFrame)
 ROOT_ADD_GTEST(dataframe_cache dataframe_cache.cxx LIBRARIES ROOTDataFrame)
 ROOT_ADD_GTEST(dataframe_callbacks dataframe_callbacks.cxx LIBRARIES ROOTDataFrame)
 ROOT_ADD_GTEST(dataframe_histomodels dataframe_histomodels.cxx LIBRARIES ROOTDataFrame)

tree/dataframe/test/dataframe_aliases.cxx → tree/dataframe/test/dataframe_colnames.cxx

@@ -2,6 +2,34 @@
 
 #include "gtest/gtest.h"
 
+
+TEST(ColNames, HasColumn)
+{
+   // From scratch
+   ROOT::RDataFrame fromScratch(1);
+
+   EXPECT_TRUE(fromScratch.HasColumn("rdfentry_"));
+   EXPECT_TRUE(fromScratch.HasColumn("rdfslot_"));
+
+   auto rdf = fromScratch.Define("def", [](){return 0;}).Alias("alias", "def");
+
+   EXPECT_TRUE(rdf.HasColumn("def"));
+   EXPECT_TRUE(rdf.HasColumn("alias"));
+
+   // From tree
+   TTree t("t","t");
+   int i;
+   t.Branch("branch", &i);
+
+   ROOT::RDataFrame fromTree(t);
+   EXPECT_TRUE(fromTree.HasColumn("branch"));
+
+   // From Source
+   auto fromSource = rdf.Cache<int>({"def"});
+   EXPECT_TRUE(fromSource.HasColumn("def"));
+
+}
+
 TEST(Aliases, DefineOnAlias)
 {
    ROOT::RDataFrame tdf(2);