Add dummy unit test for histograms to exercise "the system".

hist/hist/v7/unit/CMakeLists.txt

+if(root7)
+  ROOTTEST_ADD_UNITTEST_DIR(Hist)
+endif()
+

hist/hist/v7/unit/add.cxx

+#include "gtest/gtest.h"
+
+#include "TH1.h"
+#include "ROOT/v7/TH1.h"
+
+// Tests the number of bins
+TEST(AxisTest, NumBins) {
+  EXPECT_EQ(0, 0);
+}
+
+// Tests the axis range
+TEST(AxisTest, RangeFromTo) {
+  EXPECT_EQ(1, 1);
+}