diff --git a/internal/ceres/ordered_groups_test.cc b/internal/ceres/ordered_groups_test.cc
new file mode 100644
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+++ b/internal/ceres/ordered_groups_test.cc
@@ -0,0 +1,137 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2012 Google Inc. All rights reserved.
+// http://code.google.com/p/ceres-solver/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameeragarwal@google.com (Sameer Agarwal)
+
+#include "ceres/ordered_groups.h"
+
+#include <cstddef>
+#include <vector>
+#include "gtest/gtest.h"
+#include "ceres/collections_port.h"
+
+namespace ceres {
+namespace internal {
+
+TEST(OrderedGroup, EmptyOrderedGroupBehavesCorrectly) {
+  ParameterBlockOrdering ordering;
+  EXPECT_EQ(ordering.NumGroups(), 0);
+  EXPECT_EQ(ordering.NumElements(), 0);
+  EXPECT_EQ(ordering.GroupSize(1), 0);
+  double x;
+  EXPECT_EQ(ordering.GroupId(&x), -1);
+  EXPECT_FALSE(ordering.Remove(&x));
+}
+
+TEST(OrderedGroup, EverythingInOneGroup) {
+  ParameterBlockOrdering ordering;
+  double x[3];
+  ordering.AddElementToGroup(x, 1);
+  ordering.AddElementToGroup(x + 1, 1);
+  ordering.AddElementToGroup(x + 2, 1);
+  ordering.AddElementToGroup(x, 1);
+
+  EXPECT_EQ(ordering.NumGroups(), 1);
+  EXPECT_EQ(ordering.NumElements(), 3);
+  EXPECT_EQ(ordering.GroupSize(1), 3);
+  EXPECT_EQ(ordering.GroupSize(0), 0);
+  EXPECT_EQ(ordering.GroupId(x), 1);
+  EXPECT_EQ(ordering.GroupId(x + 1), 1);
+  EXPECT_EQ(ordering.GroupId(x + 2), 1);
+
+  ordering.Remove(x);
+  EXPECT_EQ(ordering.NumGroups(), 1);
+  EXPECT_EQ(ordering.NumElements(), 2);
+  EXPECT_EQ(ordering.GroupSize(1), 2);
+  EXPECT_EQ(ordering.GroupSize(0), 0);
+
+  EXPECT_EQ(ordering.GroupId(x), -1);
+  EXPECT_EQ(ordering.GroupId(x + 1), 1);
+  EXPECT_EQ(ordering.GroupId(x + 2), 1);
+}
+
+TEST(OrderedGroup, StartInOneGroupAndThenSplit) {
+  ParameterBlockOrdering ordering;
+  double x[3];
+  ordering.AddElementToGroup(x, 1);
+  ordering.AddElementToGroup(x + 1, 1);
+  ordering.AddElementToGroup(x + 2, 1);
+  ordering.AddElementToGroup(x, 1);
+
+  EXPECT_EQ(ordering.NumGroups(), 1);
+  EXPECT_EQ(ordering.NumElements(), 3);
+  EXPECT_EQ(ordering.GroupSize(1), 3);
+  EXPECT_EQ(ordering.GroupSize(0), 0);
+  EXPECT_EQ(ordering.GroupId(x), 1);
+  EXPECT_EQ(ordering.GroupId(x + 1), 1);
+  EXPECT_EQ(ordering.GroupId(x + 2), 1);
+
+  ordering.AddElementToGroup(x, 5);
+  EXPECT_EQ(ordering.NumGroups(), 2);
+  EXPECT_EQ(ordering.NumElements(), 3);
+  EXPECT_EQ(ordering.GroupSize(1), 2);
+  EXPECT_EQ(ordering.GroupSize(5), 1);
+  EXPECT_EQ(ordering.GroupSize(0), 0);
+
+  EXPECT_EQ(ordering.GroupId(x), 5);
+  EXPECT_EQ(ordering.GroupId(x + 1), 1);
+  EXPECT_EQ(ordering.GroupId(x + 2), 1);
+}
+
+TEST(OrderedGroup, AddAndRemoveEveryThingFromOneGroup) {
+  ParameterBlockOrdering ordering;
+  double x[3];
+  ordering.AddElementToGroup(x, 1);
+  ordering.AddElementToGroup(x + 1, 1);
+  ordering.AddElementToGroup(x + 2, 1);
+  ordering.AddElementToGroup(x, 1);
+
+  EXPECT_EQ(ordering.NumGroups(), 1);
+  EXPECT_EQ(ordering.NumElements(), 3);
+  EXPECT_EQ(ordering.GroupSize(1), 3);
+  EXPECT_EQ(ordering.GroupSize(0), 0);
+  EXPECT_EQ(ordering.GroupId(x), 1);
+  EXPECT_EQ(ordering.GroupId(x + 1), 1);
+  EXPECT_EQ(ordering.GroupId(x + 2), 1);
+
+  ordering.AddElementToGroup(x, 5);
+  ordering.AddElementToGroup(x + 1, 5);
+  ordering.AddElementToGroup(x + 2, 5);
+  EXPECT_EQ(ordering.NumGroups(), 1);
+  EXPECT_EQ(ordering.NumElements(), 3);
+  EXPECT_EQ(ordering.GroupSize(1), 0);
+  EXPECT_EQ(ordering.GroupSize(5), 3);
+  EXPECT_EQ(ordering.GroupSize(0), 0);
+
+  EXPECT_EQ(ordering.GroupId(x), 5);
+  EXPECT_EQ(ordering.GroupId(x + 1), 5);
+  EXPECT_EQ(ordering.GroupId(x + 2), 5);
+}
+
+}  // namespace internal
+}  // namespace ceres