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diff --git a/src/include/fst/equal.h b/src/include/fst/equal.h
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+// test.h
+
+// 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.
+//
+// Copyright 2005-2010 Google, Inc.
+// Author: riley@google.com (Michael Riley)
+//
+// \file
+// Function to test equality of two Fsts.
+
+#ifndef FST_LIB_EQUAL_H__
+#define FST_LIB_EQUAL_H__
+
+#include <fst/fst.h>
+
+
+namespace fst {
+
+// Tests if two Fsts have the same states and arcs in the same order.
+template<class Arc>
+bool Equal(const Fst<Arc> &fst1, const Fst<Arc> &fst2, float delta = kDelta) {
+  typedef typename Arc::StateId StateId;
+  typedef typename Arc::Weight Weight;
+
+  if (fst1.Start() != fst2.Start()) {
+    VLOG(1) << "Equal: mismatched start states";
+    return false;
+  }
+
+  StateIterator< Fst<Arc> > siter1(fst1);
+  StateIterator< Fst<Arc> > siter2(fst2);
+
+  while (!siter1.Done() || !siter2.Done()) {
+    if (siter1.Done() || siter2.Done()) {
+      VLOG(1) << "Equal: mismatched # of states";
+      return false;
+    }
+    StateId s1 = siter1.Value();
+    StateId s2 = siter2.Value();
+    if (s1 != s2) {
+      VLOG(1) << "Equal: mismatched states:"
+              << ", state1 = " << s1
+              << ", state2 = " << s2;
+      return false;
+    }
+    Weight final1 = fst1.Final(s1);
+    Weight final2 = fst2.Final(s2);
+    if (!ApproxEqual(final1, final2, delta)) {
+      VLOG(1) << "Equal: mismatched final weights:"
+              << " state = " << s1
+              << ", final1 = " << final1
+              << ", final2 = " << final2;
+      return false;
+     }
+    ArcIterator< Fst<Arc> > aiter1(fst1, s1);
+    ArcIterator< Fst<Arc> > aiter2(fst2, s2);
+    for (size_t a = 0; !aiter1.Done() || !aiter2.Done(); ++a) {
+      if (aiter1.Done() || aiter2.Done()) {
+        VLOG(1) << "Equal: mismatched # of arcs"
+                << " state = " << s1;
+        return false;
+      }
+      Arc arc1 = aiter1.Value();
+      Arc arc2 = aiter2.Value();
+      if (arc1.ilabel != arc2.ilabel) {
+        VLOG(1) << "Equal: mismatched arc input labels:"
+                << " state = " << s1
+                << ", arc = " << a
+                << ", ilabel1 = " << arc1.ilabel
+                << ", ilabel2 = " << arc2.ilabel;
+        return false;
+      } else  if (arc1.olabel != arc2.olabel) {
+        VLOG(1) << "Equal: mismatched arc output labels:"
+                << " state = " << s1
+                << ", arc = " << a
+                << ", olabel1 = " << arc1.olabel
+                << ", olabel2 = " << arc2.olabel;
+        return false;
+      } else  if (!ApproxEqual(arc1.weight, arc2.weight, delta)) {
+        VLOG(1) << "Equal: mismatched arc weights:"
+                << " state = " << s1
+                << ", arc = " << a
+                << ", weight1 = " << arc1.weight
+                << ", weight2 = " << arc2.weight;
+        return false;
+      } else  if (arc1.nextstate != arc2.nextstate) {
+        VLOG(1) << "Equal: mismatched input label:"
+                << " state = " << s1
+                << ", arc = " << a
+                << ", nextstate1 = " << arc1.nextstate
+                << ", nextstate2 = " << arc2.nextstate;
+        return false;
+      }
+      aiter1.Next();
+      aiter2.Next();
+
+    }
+    // Sanity checks: should never fail
+    if (fst1.NumArcs(s1) != fst2.NumArcs(s2) ||
+        fst1.NumInputEpsilons(s1) != fst2.NumInputEpsilons(s2) ||
+        fst1.NumOutputEpsilons(s1) != fst2.NumOutputEpsilons(s2)) {
+      FSTERROR() << "Equal: inconsistent arc/epsilon counts";
+    }
+
+    siter1.Next();
+    siter2.Next();
+  }
+  return true;
+}
+
+}  // namespace fst
+
+
+#endif  // FST_LIB_EQUAL_H__