diff --git a/tests/testPreconditioner.cpp b/tests/testPreconditioner.cpp
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+++ b/tests/testPreconditioner.cpp
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+/* ----------------------------------------------------------------------------
+
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation,
+ * Atlanta, Georgia 30332-0415
+ * All Rights Reserved
+ * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
+
+ * See LICENSE for the license information
+
+ * -------------------------------------------------------------------------- */
+
+/**
+ *  @file   testPreconditioner.cpp
+ *  @brief  Unit tests for Preconditioners
+ *  @author Sungtae An
+ *  @date   Nov 6, 2014
+ **/
+
+#include <CppUnitLite/TestHarness.h>
+
+#include <gtsam/linear/GaussianFactorGraph.h>
+#include <gtsam/linear/Preconditioner.h>
+#include <gtsam/nonlinear/Values.h>
+#include <gtsam/geometry/Point2.h>
+#include <gtsam/linear/PCGSolver.h>
+
+using namespace std;
+using namespace gtsam;
+
+/* ************************************************************************* */
+static GaussianFactorGraph createSimpleGaussianFactorGraph() {
+  GaussianFactorGraph fg;
+  SharedDiagonal unit2 = noiseModel::Unit::Create(2);
+  // linearized prior on x1: c[_x1_]+x1=0 i.e. x1=-c[_x1_]
+  fg += JacobianFactor(2, 10*eye(2), -1.0*ones(2), unit2);
+  // odometry between x1 and x2: x2-x1=[0.2;-0.1]
+  fg += JacobianFactor(2, -10*eye(2), 0, 10*eye(2), (Vector(2) << 2.0, -1.0), unit2);
+  // measurement between x1 and l1: l1-x1=[0.0;0.2]
+  fg += JacobianFactor(2, -5*eye(2), 1, 5*eye(2), (Vector(2) << 0.0, 1.0), unit2);
+  // measurement between x2 and l1: l1-x2=[-0.2;0.3]
+  fg += JacobianFactor(0, -5*eye(2), 1, 5*eye(2), (Vector(2) << -1.0, 1.5), unit2);
+  return fg;
+}
+
+/* ************************************************************************* */
+// Copy of BlockJacobiPreconditioner::build
+std::vector<Matrix> buildBlocks( const GaussianFactorGraph &gfg, const KeyInfo &keyInfo)
+{
+  const size_t n = keyInfo.size();
+  std::vector<size_t> dims_ = keyInfo.colSpec();
+
+  /* prepare the buffer of block diagonals */
+  std::vector<Matrix> blocks; blocks.reserve(n);
+
+  /* allocate memory for the factorization of block diagonals */
+  size_t nnz = 0;
+  for ( size_t i = 0 ; i < n ; ++i ) {
+    const size_t dim = dims_[i];
+    blocks.push_back(Matrix::Zero(dim, dim));
+    // nnz += (((dim)*(dim+1)) >> 1); // d*(d+1) / 2  ;
+    nnz += dim*dim;
+  }
+
+  /* compute the block diagonal by scanning over the factors */
+  BOOST_FOREACH ( const GaussianFactor::shared_ptr &gf, gfg ) {
+    if ( JacobianFactor::shared_ptr jf = boost::dynamic_pointer_cast<JacobianFactor>(gf) ) {
+      for ( JacobianFactor::const_iterator it = jf->begin() ; it != jf->end() ; ++it ) {
+        const KeyInfoEntry &entry =  keyInfo.find(*it)->second;
+        const Matrix &Ai = jf->getA(it);
+        blocks[entry.index()] += (Ai.transpose() * Ai);
+      }
+    }
+    else if ( HessianFactor::shared_ptr hf = boost::dynamic_pointer_cast<HessianFactor>(gf) ) {
+      for ( HessianFactor::const_iterator it = hf->begin() ; it != hf->end() ; ++it ) {
+        const KeyInfoEntry &entry =  keyInfo.find(*it)->second;
+        const Matrix &Hii = hf->info(it, it).selfadjointView();
+        blocks[entry.index()] += Hii;
+      }
+    }
+    else {
+      throw invalid_argument("BlockJacobiPreconditioner::build gfg contains a factor that is neither a JacobianFactor nor a HessianFactor.");
+    }
+  }
+
+  return blocks;
+}
+
+/* ************************************************************************* */
+TEST( Preconditioner, buildBlocks ) {
+  // Create simple Gaussian factor graph and initial values
+  GaussianFactorGraph gfg = createSimpleGaussianFactorGraph();
+  Values initial;
+  initial.insert(0,Point2(4, 5));
+  initial.insert(1,Point2(0,  1));
+  initial.insert(2,Point2(-5, 7));
+
+  // Expected Hessian block diagonal matrices
+  std::map<Key, Matrix> expectedHessian =gfg.hessianBlockDiagonal();
+
+  // Actual Hessian block diagonal matrices from BlockJacobiPreconditioner::build
+  std::vector<Matrix> actualHessian = buildBlocks(gfg, KeyInfo(gfg));
+
+  // Compare the number of block diagonal matrices
+  EXPECT_LONGS_EQUAL(expectedHessian.size(), actualHessian.size());
+
+  // Compare the values of matrices
+  std::map<Key, Matrix>::const_iterator it1 = expectedHessian.begin();
+  std::vector<Matrix>::const_iterator it2 = actualHessian.begin();
+  for(; it1!=expectedHessian.end(); it1++, it2++)
+    EXPECT(assert_equal(it1->second, *it2));
+}
+
+/* ************************************************************************* */
+int main() { TestResult tr; return TestRegistry::runAllTests(tr); }
+/* ************************************************************************* */