Add tests for bin numer calculation.

hist/hist/v7/test/binning.cxx

+#include "gtest/gtest.h"
+#include "ROOT/THist.hxx"
+#include "ROOT/THistBinIter.hxx"
+#include <cmath>
+#include <limits>
+
+using namespace ROOT::Experimental;
+
+// Test FindBin() in all its glory.
+
+// Basic binning on a Equidistant axis.
+TEST(AxisBinning, EquiDistBasic) {
+   TAxisEquidistant ax("TITLE", 10, -1., 1.);
+   EXPECT_EQ(1, ax.FindBin(-.999));
+   EXPECT_EQ(5, ax.FindBin(-.001));
+   EXPECT_EQ(10, ax.FindBin(0.999));
+   EXPECT_EQ(0, ax.FindBin(-2.));
+   EXPECT_EQ(11, ax.FindBin(2000.));
+
+   EXPECT_GE(6, ax.FindBin(std::numeric_limits<double>::min()));
+   EXPECT_LE(5, ax.FindBin(std::numeric_limits<double>::min()));
+   EXPECT_GE(6, ax.FindBin(-std::numeric_limits<double>::min()));
+   EXPECT_LE(5, ax.FindBin(-std::numeric_limits<double>::min()));
+
+   EXPECT_EQ(11, ax.FindBin(std::numeric_limits<double>::max()));
+   EXPECT_EQ(0, ax.FindBin(-std::numeric_limits<double>::max()));
+}
+
+// Epsilon bin widths.
+TEST(AxisBinning, EquiDistEps) {
+   static constexpr auto eps = std::numeric_limits<double>::epsilon();
+   TAxisEquidistant ax("TITLE", 10, 0., eps * 10.);
+   EXPECT_LE(0, ax.FindBin(0.5*eps));
+   EXPECT_GE(1, ax.FindBin(0.5*eps));
+
+   EXPECT_LE(5, ax.FindBin(5.*eps));
+   EXPECT_GE(6, ax.FindBin(5.*eps));
+
+   EXPECT_LE(10, ax.FindBin(10.*eps));
+   EXPECT_GE(11, ax.FindBin(10.*eps));
+
+   EXPECT_EQ(0, ax.FindBin(-2000.*eps));
+   EXPECT_EQ(11, ax.FindBin(2000.*eps));
+   EXPECT_EQ(1, ax.FindBin(std::numeric_limits<double>::min()));
+   EXPECT_EQ(0, ax.FindBin(-std::numeric_limits<double>::min()));
+   EXPECT_EQ(11, ax.FindBin(std::numeric_limits<double>::max()));
+   EXPECT_EQ(0, ax.FindBin(-std::numeric_limits<double>::max()));
+}