diff --git a/src/shogun/statistical_testing/QuadraticTimeMMD.cpp b/src/shogun/statistical_testing/QuadraticTimeMMD.cpp
index acde91a22e2..ec7203a0fef 100644
--- a/src/shogun/statistical_testing/QuadraticTimeMMD.cpp
+++ b/src/shogun/statistical_testing/QuadraticTimeMMD.cpp
@@ -287,6 +287,12 @@ CQuadraticTimeMMD::~CQuadraticTimeMMD()
 	get_kernel_manager().restore_kernel_at(0);
 }
 
+void CQuadraticTimeMMD::set_kernel(CKernel* kernel)
+{
+	CTwoSampleTest::set_kernel(kernel);
+	self->is_kernel_initialized=false;
+}
+
 const std::function<float32_t(SGMatrix<float32_t>)> CQuadraticTimeMMD::get_direct_estimation_method() const
 {
 	return FullDirect();
diff --git a/src/shogun/statistical_testing/QuadraticTimeMMD.h b/src/shogun/statistical_testing/QuadraticTimeMMD.h
index 869534f1d4a..18570381436 100644
--- a/src/shogun/statistical_testing/QuadraticTimeMMD.h
+++ b/src/shogun/statistical_testing/QuadraticTimeMMD.h
@@ -49,6 +49,7 @@ class CQuadraticTimeMMD : public CMMD
 	CQuadraticTimeMMD(CFeatures* samples_from_p, CFeatures* samples_from_q);
 
 	virtual ~CQuadraticTimeMMD();
+	virtual void set_kernel(CKernel* kernel);
 
 	virtual float64_t compute_statistic();
 	virtual float64_t compute_variance();
diff --git a/src/shogun/statistical_testing/TwoSampleTest.cpp b/src/shogun/statistical_testing/TwoSampleTest.cpp
index 7d85bbffd3d..a5d98f5a95d 100644
--- a/src/shogun/statistical_testing/TwoSampleTest.cpp
+++ b/src/shogun/statistical_testing/TwoSampleTest.cpp
@@ -34,13 +34,14 @@ CTwoSampleTest::~CTwoSampleTest()
 
 void CTwoSampleTest::set_kernel(CKernel* kernel)
 {
-	auto& km = get_kernel_manager();
-	km.kernel_at(0) = kernel;
+	auto& km=get_kernel_manager();
+	km.kernel_at(0)=kernel;
+	km.restore_kernel_at(0);
 }
 
 CKernel* CTwoSampleTest::get_kernel() const
 {
-	const auto& km = get_kernel_manager();
+	const auto& km=get_kernel_manager();
 	return km.kernel_at(0);
 }
 
diff --git a/src/shogun/statistical_testing/TwoSampleTest.h b/src/shogun/statistical_testing/TwoSampleTest.h
index 865acdcb0a2..f8008ce72fd 100644
--- a/src/shogun/statistical_testing/TwoSampleTest.h
+++ b/src/shogun/statistical_testing/TwoSampleTest.h
@@ -32,7 +32,7 @@ class CTwoSampleTest : public CTwoDistributionTest
 	CTwoSampleTest();
 	virtual ~CTwoSampleTest();
 
-	void set_kernel(CKernel* kernel);
+	virtual void set_kernel(CKernel* kernel);
 	CKernel* get_kernel() const;
 
 	virtual float64_t compute_statistic() = 0;
diff --git a/src/shogun/statistical_testing/internals/DataFetcher.cpp b/src/shogun/statistical_testing/internals/DataFetcher.cpp
index c2cb3693b9a..b770b9e7de1 100644
--- a/src/shogun/statistical_testing/internals/DataFetcher.cpp
+++ b/src/shogun/statistical_testing/internals/DataFetcher.cpp
@@ -65,8 +65,10 @@ float64_t DataFetcher::get_train_test_ratio() const
 
 void DataFetcher::set_train_mode(bool train_mode)
 {
+	m_train_test_details.train_mode=train_mode;
+	// TODO put the following in another methods
 	index_t start_index=0;
-	if (train_mode)
+	if (m_train_test_details.train_mode)
 	{
 		m_num_samples=m_train_test_details.get_num_training_samples();
 		if (m_num_samples==0)
@@ -107,18 +109,46 @@ void DataFetcher::set_xvalidation_mode(bool xvalidation_mode)
 
 index_t DataFetcher::get_num_folds() const
 {
-//	REQUIRE(fetchers[0]!=nullptr, "Please set the samples first!\n");
-//	return fetchers[0]->get_train_test_ratio();
-	return 0;
+	return 1+ceil(get_train_test_ratio());
 }
 
 void DataFetcher::use_fold(index_t idx)
 {
-//	using fetcher_type=std::unique_ptr<DataFetcher>;
-//	std::for_each(fetchers.begin(), fetchers.end(), [&train_mode](fetcher_type& f)
-//	{
-//		f->use_fold(idx);
-//	});
+	auto num_folds=get_num_folds();
+	REQUIRE(idx>=0, "The index (%d) has to be between 0 and %d, both inclusive!\n", idx, num_folds-1);
+	REQUIRE(idx<num_folds, "The index (%d) has to be between 0 and %d, both inclusive!\n", idx, num_folds-1);
+
+	auto num_per_fold=m_train_test_details.get_total_num_samples()/num_folds;
+
+	if (train_test_subset_used)
+		m_samples->remove_subset();
+
+	SGVector<index_t> inds;
+	auto start_idx=idx*num_per_fold;
+	auto num_samples=0;
+
+	if (m_train_test_details.train_mode)
+	{
+		num_samples=m_train_test_details.get_num_training_samples();
+		inds=SGVector<index_t>(num_samples);
+		std::iota(inds.data(), inds.data()+inds.size(), 0);
+		if (start_idx<inds.size())
+		{
+			std::for_each(inds.data()+start_idx, inds.data()+inds.size(), [&num_per_fold](index_t& val)
+			{
+				val+=num_per_fold;
+			});
+		}
+	}
+	else
+	{
+		num_samples=m_train_test_details.get_num_test_samples();
+		inds=SGVector<index_t>(num_samples);
+		std::iota(inds.data(), inds.data()+inds.size(), start_idx);
+		m_samples->add_subset(inds);
+	}
+	inds.display_vector("inds");
+	m_samples->add_subset(inds);
 }
 
 void DataFetcher::set_blockwise(bool blockwise)
diff --git a/src/shogun/statistical_testing/internals/DataManager.cpp b/src/shogun/statistical_testing/internals/DataManager.cpp
index 1a3a7db588e..6ba4b9629fa 100644
--- a/src/shogun/statistical_testing/internals/DataManager.cpp
+++ b/src/shogun/statistical_testing/internals/DataManager.cpp
@@ -256,7 +256,7 @@ void DataManager::set_xvalidation_mode(bool xvalidation_mode)
 index_t DataManager::get_num_folds() const
 {
 	REQUIRE(fetchers[0]!=nullptr, "Please set the samples first!\n");
-	return fetchers[0]->get_train_test_ratio();
+	return fetchers[0]->get_num_folds();
 }
 
 void DataManager::use_fold(index_t idx)
diff --git a/tests/unit/statistical_testing/KernelSelectionMaxXValidation_unittest.cc b/tests/unit/statistical_testing/KernelSelectionMaxXValidation_unittest.cc
new file mode 100644
index 00000000000..1b4ea1f29a4
--- /dev/null
+++ b/tests/unit/statistical_testing/KernelSelectionMaxXValidation_unittest.cc
@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) The Shogun Machine Learning Toolbox
+ * Written (W) 2012-2013 Heiko Strathmann
+ * Written (w) 2016 Soumyajit De
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ * 2. 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.
+ *
+ * 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.
+ *
+ * The views and conclusions contained in the software and documentation are those
+ * of the authors and should not be interpreted as representing official policies,
+ * either expressed or implied, of the Shogun Development Team.
+ */
+
+#include <shogun/base/some.h>
+#include <shogun/kernel/GaussianKernel.h>
+#include <shogun/kernel/CombinedKernel.h>
+#include <shogun/features/DenseFeatures.h>
+#include <shogun/features/streaming/generators/MeanShiftDataGenerator.h>
+#include <shogun/mathematics/Statistics.h>
+#include <shogun/mathematics/eigen3.h>
+#include <shogun/mathematics/Math.h>
+#include <shogun/statistical_testing/QuadraticTimeMMD.h>
+#include <gtest/gtest.h>
+
+using namespace shogun;
+
+TEST(KernelSelectionMaxXValidation, single_kernel)
+{
+	const index_t m=10;
+	const index_t n=15;
+	const index_t dim=2;
+	const float64_t difference=0.5;
+	const index_t num_kernels=10;
+
+//	sg_io->set_loglevel(MSG_DEBUG);
+//	sg_io->set_location_info(MSG_FUNCTION);
+
+	// use fixed seed
+	sg_rand->set_seed(12345);
+
+	// streaming data generator for mean shift distributions
+	auto gen_p=new CMeanShiftDataGenerator(0, dim, 0);
+	auto gen_q=new CMeanShiftDataGenerator(difference, dim, 0);
+
+	auto feats_p=gen_p->get_streamed_features(m);
+	auto feats_q=gen_q->get_streamed_features(n);
+
+	SG_UNREF(gen_p);
+	SG_UNREF(gen_q);
+
+	// create MMD instance, convienience constructor
+	auto mmd=some<CQuadraticTimeMMD>(feats_p, feats_q);
+	mmd->set_statistic_type(ST_BIASED_FULL);
+
+	for (auto i=0; i<num_kernels; ++i)
+	{
+		// shoguns kernel width is different
+		float64_t sigma=(i+1)*0.5;
+		float64_t sq_sigma_twice=sigma*sigma*2;
+		mmd->add_kernel(new CGaussianKernel(10, sq_sigma_twice));
+	}
+
+	mmd->select_kernel(KSM_MAXIMIZE_XVALIDATION, false, 4, 1, 0.05);
+	auto selected_kernel=static_cast<CGaussianKernel*>(mmd->get_kernel());
+	EXPECT_NEAR(selected_kernel->get_width(), 0.5, 1E-10);
+}