diff --git a/cartographer/mapping/internal/testing/fake_trimmable.h b/cartographer/mapping/internal/testing/fake_trimmable.h
new file mode 100644
index 0000000..c86066d
--- /dev/null
+++ b/cartographer/mapping/internal/testing/fake_trimmable.h
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2018 The Cartographer Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace cartographer {
+namespace mapping {
+namespace testing {
+
+class FakeTrimmable : public Trimmable {
+ public:
+  FakeTrimmable(int trajectory_id, int num_submaps) {
+    for (int index = 0; index < num_submaps; ++index) {
+      submaps_.push_back(SubmapId{trajectory_id, index});
+    }
+  }
+  ~FakeTrimmable() override {}
+
+  int num_submaps(const int trajectory_id) const override {
+    return submaps_.size() - trimmed_submaps_.size();
+  }
+
+  std::vector<SubmapId> GetSubmapIds(int trajectory_id) const override {
+    return submaps_;
+  }
+
+  MapById<SubmapId, PoseGraphInterface::SubmapData> GetAllSubmapData()
+      const override {
+    return {};
+  }
+
+  MapById<NodeId, TrajectoryNode> GetTrajectoryNodes() const override {
+    return {};
+  }
+
+  std::vector<PoseGraphInterface::Constraint> GetConstraints() const override {
+    return {};
+  }
+
+  void MarkSubmapAsTrimmed(const SubmapId& submap_id) override {
+    trimmed_submaps_.push_back(submap_id);
+  }
+
+  bool IsFinished(const int trajectory_id) const override { return false; }
+
+  std::vector<SubmapId> trimmed_submaps() { return trimmed_submaps_; }
+
+ private:
+  std::vector<SubmapId> submaps_;
+  std::vector<SubmapId> trimmed_submaps_;
+};
+
+}  // namespace testing
+}  // namespace mapping
+}  // namespace cartographer
diff --git a/cartographer/mapping/pose_graph_trimmer_test.cc b/cartographer/mapping/pose_graph_trimmer_test.cc
index d780f6d..daad1bc 100644
--- a/cartographer/mapping/pose_graph_trimmer_test.cc
+++ b/cartographer/mapping/pose_graph_trimmer_test.cc
@@ -19,59 +19,17 @@
 #include <vector>
 
 #include "cartographer/mapping/id.h"
+#include "cartographer/mapping/internal/testing/fake_trimmable.h"
 #include "gtest/gtest.h"
 
 namespace cartographer {
 namespace mapping {
 namespace {
 
-class FakePoseGraph : public Trimmable {
- public:
-  FakePoseGraph(int trajectory_id, int num_submaps) {
-    for (int index = 0; index < num_submaps; ++index) {
-      submaps_.push_back(SubmapId{trajectory_id, index});
-    }
-  }
-  ~FakePoseGraph() override {}
-
-  int num_submaps(const int trajectory_id) const override {
-    return submaps_.size() - trimmed_submaps_.size();
-  }
-
-  std::vector<SubmapId> GetSubmapIds(int trajectory_id) const override {
-    return submaps_;
-  }
-
-  MapById<SubmapId, PoseGraphInterface::SubmapData> GetAllSubmapData()
-      const override {
-    return {};
-  }
-
-  MapById<NodeId, TrajectoryNode> GetTrajectoryNodes() const override {
-    return {};
-  }
-
-  std::vector<PoseGraphInterface::Constraint> GetConstraints() const override {
-    return {};
-  }
-
-  void MarkSubmapAsTrimmed(const SubmapId& submap_id) override {
-    trimmed_submaps_.push_back(submap_id);
-  }
-
-  bool IsFinished(const int trajectory_id) const override { return false; }
-
-  std::vector<SubmapId> trimmed_submaps() { return trimmed_submaps_; }
-
- private:
-  std::vector<SubmapId> submaps_;
-  std::vector<SubmapId> trimmed_submaps_;
-};
-
 TEST(PureLocalizationTrimmerTest, MarksSubmapsAsExpected) {
   const int kTrajectoryId = 42;
   PureLocalizationTrimmer trimmer(kTrajectoryId, 15);
-  FakePoseGraph fake_pose_graph(kTrajectoryId, 17);
+  testing::FakeTrimmable fake_pose_graph(kTrajectoryId, 17);
   trimmer.Trim(&fake_pose_graph);
 
   const auto trimmed_submaps = fake_pose_graph.trimmed_submaps();