diff --git a/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDecider.java b/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDecider.java
index c28a0a2a582..0c8049da870 100644
--- a/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDecider.java
+++ b/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDecider.java
@@ -36,7 +36,6 @@ import org.elasticsearch.common.unit.RatioValue;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.node.settings.NodeSettingsService;
 
-import java.util.List;
 import java.util.Map;
 
 import static org.elasticsearch.cluster.InternalClusterInfoService.shardIdentifierFromRouting;
@@ -220,6 +219,46 @@ public class DiskThresholdDecider extends AllocationDecider {
         infoService.addListener(new DiskListener(client));
     }
 
+    // For Testing
+    ApplySettings newApplySettings() {
+        return new ApplySettings();
+    }
+
+    // For Testing
+    public Double getFreeDiskThresholdLow() {
+        return freeDiskThresholdLow;
+    }
+
+    // For Testing
+    public Double getFreeDiskThresholdHigh() {
+        return freeDiskThresholdHigh;
+    }
+
+    // For Testing
+    public ByteSizeValue getFreeBytesThresholdLow() {
+        return freeBytesThresholdLow;
+    }
+
+    // For Testing
+    public ByteSizeValue getFreeBytesThresholdHigh() {
+        return freeBytesThresholdHigh;
+    }
+
+    // For Testing
+    public boolean isIncludeRelocations() {
+        return includeRelocations;
+    }
+
+    // For Testing
+    public boolean isEnabled() {
+        return enabled;
+    }
+
+    // For Testing
+    public TimeValue getRerouteInterval() {
+        return rerouteInterval;
+    }
+
     /**
      * Returns the size of all shards that are currently being relocated to
      * the node, but may not be finished transfering yet.
diff --git a/src/test/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDeciderUnitTests.java b/src/test/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDeciderUnitTests.java
new file mode 100644
index 00000000000..3809a9f7b27
--- /dev/null
+++ b/src/test/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDeciderUnitTests.java
@@ -0,0 +1,96 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.
+ */
+
+package org.elasticsearch.cluster.routing.allocation.decider;
+
+import com.google.common.collect.ImmutableMap;
+import org.elasticsearch.cluster.ClusterInfo;
+import org.elasticsearch.cluster.ClusterInfoService;
+import org.elasticsearch.cluster.DiskUsage;
+import org.elasticsearch.common.settings.ImmutableSettings;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.ByteSizeValue;
+import org.elasticsearch.node.settings.NodeSettingsService;
+import org.elasticsearch.test.ElasticsearchTestCase;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+
+/**
+ * Unit tests for the DiskThresholdDecider
+ */
+public class DiskThresholdDeciderUnitTests extends ElasticsearchTestCase {
+
+    @Test
+    public void testDynamicSettings() {
+        NodeSettingsService nss = new NodeSettingsService(ImmutableSettings.EMPTY);
+
+        ClusterInfoService cis = new ClusterInfoService() {
+            @Override
+            public ClusterInfo getClusterInfo() {
+                Map<String, DiskUsage> usages = new HashMap<>();
+                Map<String, Long> shardSizes = new HashMap<>();
+                return new ClusterInfo(ImmutableMap.copyOf(usages), ImmutableMap.copyOf(shardSizes));
+            }
+
+            @Override
+            public void addListener(Listener listener) {
+                // noop
+            }
+        };
+        DiskThresholdDecider decider = new DiskThresholdDecider(ImmutableSettings.EMPTY, nss, cis, null);
+
+        assertThat(decider.getFreeBytesThresholdHigh(), equalTo(ByteSizeValue.parseBytesSizeValue("0b")));
+        assertThat(decider.getFreeDiskThresholdHigh(), equalTo(10.0d));
+        assertThat(decider.getFreeBytesThresholdLow(), equalTo(ByteSizeValue.parseBytesSizeValue("0b")));
+        assertThat(decider.getFreeDiskThresholdLow(), equalTo(15.0d));
+        assertThat(decider.getRerouteInterval().seconds(), equalTo(60L));
+        assertTrue(decider.isEnabled());
+        assertTrue(decider.isIncludeRelocations());
+
+        DiskThresholdDecider.ApplySettings applySettings = decider.newApplySettings();
+
+        Settings newSettings = ImmutableSettings.builder()
+                .put(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED, false)
+                .put(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_INCLUDE_RELOCATIONS, false)
+                .put(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_WATERMARK, "70%")
+                .put(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_LOW_DISK_WATERMARK, "500mb")
+                .put(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_REROUTE_INTERVAL, "30s")
+                .build();
+
+        applySettings.onRefreshSettings(newSettings);
+
+        assertThat("high threshold bytes should be unset",
+                decider.getFreeBytesThresholdHigh(), equalTo(ByteSizeValue.parseBytesSizeValue("0b")));
+        assertThat("high threshold percentage should be changed",
+                decider.getFreeDiskThresholdHigh(), equalTo(30.0d));
+        assertThat("low threshold bytes should be set to 500mb",
+                decider.getFreeBytesThresholdLow(), equalTo(ByteSizeValue.parseBytesSizeValue("500mb")));
+        assertThat("low threshold bytes should be unset",
+                decider.getFreeDiskThresholdLow(), equalTo(0.0d));
+        assertThat("reroute interval should be changed to 30 seconds",
+                decider.getRerouteInterval().seconds(), equalTo(30L));
+        assertFalse("disk threshold decider should now be disabled", decider.isEnabled());
+        assertFalse("relocations should now be disabled", decider.isIncludeRelocations());
+    }
+
+}