diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
index 096ca09..e5ec449 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
@@ -27,12 +27,15 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Stack;
 
 public final class BinaryDictIOUtils {
     private static final boolean DBG = false;
+    private static final int MSB24 = 0x800000;
+    private static final int SINT24_MAX = 0x7FFFFF;
     private static final int MAX_JUMPS = 10000;
 
     private BinaryDictIOUtils() {
@@ -646,4 +649,302 @@
         writeSInt24ToStream(destination, FormatSpec.NO_FORWARD_LINK_ADDRESS);
         return size + FormatSpec.FORWARD_LINK_ADDRESS_SIZE;
     }
+
+    /**
+     * Move a group that is referred to by oldGroupOrigin to the tail of the file.
+     * And set the children address to the byte after the group.
+     *
+     * @param nodeOrigin the address of the tail of the file.
+     * @param characters
+     * @param length
+     * @param flags
+     * @param frequency
+     * @param parentAddress
+     * @param shortcutTargets
+     * @param bigrams
+     * @param destination the stream representing the tail of the file.
+     * @param buffer the buffer representing the (constant-size) body of the file.
+     * @param oldNodeOrigin
+     * @param oldGroupOrigin
+     * @param formatOptions
+     * @return the size written, in bytes.
+     * @throws IOException
+     */
+    private static int moveGroup(final int nodeOrigin, final int[] characters, final int length,
+            final int flags, final int frequency, final int parentAddress,
+            final ArrayList<WeightedString> shortcutTargets,
+            final ArrayList<PendingAttribute> bigrams, final OutputStream destination,
+            final FusionDictionaryBufferInterface buffer, final int oldNodeOrigin,
+            final int oldGroupOrigin, final FormatOptions formatOptions) throws IOException {
+        int size = 0;
+        final int newGroupOrigin = nodeOrigin + 1;
+        final int[] writtenCharacters = Arrays.copyOfRange(characters, 0, length);
+        final CharGroupInfo tmpInfo = new CharGroupInfo(newGroupOrigin, -1 /* endAddress */,
+                flags, writtenCharacters, frequency, parentAddress, FormatSpec.NO_CHILDREN_ADDRESS,
+                shortcutTargets, bigrams);
+        size = computeGroupSize(tmpInfo, formatOptions);
+        final CharGroupInfo newInfo = new CharGroupInfo(newGroupOrigin, newGroupOrigin + size,
+                flags, writtenCharacters, frequency, parentAddress,
+                nodeOrigin + 1 + size + FormatSpec.FORWARD_LINK_ADDRESS_SIZE, shortcutTargets,
+                bigrams);
+        moveCharGroup(destination, buffer, newInfo, oldNodeOrigin, oldGroupOrigin, formatOptions);
+        return 1 + size + FormatSpec.FORWARD_LINK_ADDRESS_SIZE;
+    }
+
+    /**
+     * Insert a word into a binary dictionary.
+     *
+     * @param buffer
+     * @param destination
+     * @param word
+     * @param frequency
+     * @param bigramStrings
+     * @param shortcuts
+     * @throws IOException
+     * @throws UnsupportedFormatException
+     */
+    // TODO: Support batch insertion.
+    public static void insertWord(final FusionDictionaryBufferInterface buffer,
+            final OutputStream destination, final String word, final int frequency,
+            final ArrayList<WeightedString> bigramStrings,
+            final ArrayList<WeightedString> shortcuts, final boolean isNotAWord,
+            final boolean isBlackListEntry)
+                    throws IOException, UnsupportedFormatException {
+        final ArrayList<PendingAttribute> bigrams = new ArrayList<PendingAttribute>();
+        if (bigramStrings != null) {
+            for (final WeightedString bigram : bigramStrings) {
+                int position = getTerminalPosition(buffer, bigram.mWord);
+                if (position == FormatSpec.NOT_VALID_WORD) {
+                    // TODO: figure out what is the correct thing to do here.
+                } else {
+                    bigrams.add(new PendingAttribute(position, bigram.mFrequency));
+                }
+            }
+        }
+
+        final boolean isTerminal = true;
+        final boolean hasBigrams = !bigrams.isEmpty();
+        final boolean hasShortcuts = shortcuts != null && !shortcuts.isEmpty();
+
+        // find the insert position of the word.
+        if (buffer.position() != 0) buffer.position(0);
+        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
+
+        int wordPos = 0, address = buffer.position(), nodeOriginAddress = buffer.position();
+        final int[] codePoints = FusionDictionary.getCodePoints(word);
+        final int wordLen = codePoints.length;
+
+        for (int depth = 0; depth < Constants.Dictionary.MAX_WORD_LENGTH; ++depth) {
+            if (wordPos >= wordLen) break;
+            nodeOriginAddress = buffer.position();
+            int nodeParentAddress = -1;
+            final int charGroupCount = BinaryDictInputOutput.readCharGroupCount(buffer);
+            boolean foundNextGroup = false;
+
+            for (int i = 0; i < charGroupCount; ++i) {
+                address = buffer.position();
+                final CharGroupInfo currentInfo = BinaryDictInputOutput.readCharGroup(buffer,
+                        buffer.position(), header.mFormatOptions);
+                final boolean isMovedGroup = BinaryDictInputOutput.isMovedGroup(currentInfo.mFlags,
+                        header.mFormatOptions);
+                if (isMovedGroup) continue;
+                nodeParentAddress = (currentInfo.mParentAddress == FormatSpec.NO_PARENT_ADDRESS)
+                        ? FormatSpec.NO_PARENT_ADDRESS : currentInfo.mParentAddress + address;
+                boolean matched = true;
+                for (int p = 0; p < currentInfo.mCharacters.length; ++p) {
+                    if (wordPos + p >= wordLen) {
+                        /*
+                         * splitting
+                         * before
+                         *  abcd - ef
+                         *
+                         * insert "abc"
+                         *
+                         * after
+                         *  abc - d - ef
+                         */
+                        final int newNodeAddress = buffer.limit();
+                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(p > 1,
+                                isTerminal, 0, hasShortcuts, hasBigrams, false /* isNotAWord */,
+                                false /* isBlackListEntry */, header.mFormatOptions);
+                        int written = moveGroup(newNodeAddress, currentInfo.mCharacters, p, flags,
+                                frequency, nodeParentAddress, shortcuts, bigrams, destination,
+                                buffer, nodeOriginAddress, address, header.mFormatOptions);
+
+                        final int[] characters2 = Arrays.copyOfRange(currentInfo.mCharacters, p,
+                                currentInfo.mCharacters.length);
+                        if (currentInfo.mChildrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
+                            updateParentAddresses(buffer, currentInfo.mChildrenAddress,
+                                    newNodeAddress + written + 1, header.mFormatOptions);
+                        }
+                        final CharGroupInfo newInfo2 = new CharGroupInfo(
+                                newNodeAddress + written + 1, -1 /* endAddress */,
+                                currentInfo.mFlags, characters2, currentInfo.mFrequency,
+                                newNodeAddress + 1, currentInfo.mChildrenAddress,
+                                currentInfo.mShortcutTargets, currentInfo.mBigrams);
+                        writeNode(destination, new CharGroupInfo[] { newInfo2 });
+                        return;
+                    } else if (codePoints[wordPos + p] != currentInfo.mCharacters[p]) {
+                        if (p > 0) {
+                            /*
+                             * splitting
+                             * before
+                             *   ab - cd
+                             *
+                             * insert "ac"
+                             *
+                             * after
+                             *   a - b - cd
+                             *     |
+                             *     - c
+                             */
+
+                            final int newNodeAddress = buffer.limit();
+                            final int childrenAddress = currentInfo.mChildrenAddress;
+
+                            // move prefix
+                            final int prefixFlags = BinaryDictInputOutput.makeCharGroupFlags(p > 1,
+                                    false /* isTerminal */, 0 /* childrenAddressSize*/,
+                                    false /* hasShortcut */, false /* hasBigrams */,
+                                    false /* isNotAWord */, false /* isBlackListEntry */,
+                                    header.mFormatOptions);
+                            int written = moveGroup(newNodeAddress, currentInfo.mCharacters, p,
+                                    prefixFlags, -1 /* frequency */, nodeParentAddress, null, null,
+                                    destination, buffer, nodeOriginAddress, address,
+                                    header.mFormatOptions);
+
+                            final int[] suffixCharacters = Arrays.copyOfRange(
+                                    currentInfo.mCharacters, p, currentInfo.mCharacters.length);
+                            if (currentInfo.mChildrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
+                                updateParentAddresses(buffer, currentInfo.mChildrenAddress,
+                                        newNodeAddress + written + 1, header.mFormatOptions);
+                            }
+                            final int suffixFlags = BinaryDictInputOutput.makeCharGroupFlags(
+                                    suffixCharacters.length > 1,
+                                    (currentInfo.mFlags & FormatSpec.FLAG_IS_TERMINAL) != 0,
+                                    0 /* childrenAddressSize */,
+                                    (currentInfo.mFlags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS)
+                                            != 0,
+                                    (currentInfo.mFlags & FormatSpec.FLAG_HAS_BIGRAMS) != 0,
+                                    isNotAWord, isBlackListEntry, header.mFormatOptions);
+                            final CharGroupInfo suffixInfo = new CharGroupInfo(
+                                    newNodeAddress + written + 1, -1 /* endAddress */, suffixFlags,
+                                    suffixCharacters, currentInfo.mFrequency, newNodeAddress + 1,
+                                    currentInfo.mChildrenAddress, currentInfo.mShortcutTargets,
+                                    currentInfo.mBigrams);
+                            written += computeGroupSize(suffixInfo, header.mFormatOptions) + 1;
+
+                            final int[] newCharacters = Arrays.copyOfRange(codePoints, wordPos + p,
+                                    codePoints.length);
+                            final int flags = BinaryDictInputOutput.makeCharGroupFlags(
+                                    newCharacters.length > 1, isTerminal,
+                                    0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
+                                    isNotAWord, isBlackListEntry, header.mFormatOptions);
+                            final CharGroupInfo newInfo = new CharGroupInfo(
+                                    newNodeAddress + written, -1 /* endAddress */, flags,
+                                    newCharacters, frequency, newNodeAddress + 1,
+                                    FormatSpec.NO_CHILDREN_ADDRESS, shortcuts, bigrams);
+                            writeNode(destination, new CharGroupInfo[] { suffixInfo, newInfo });
+                            return;
+                        }
+                        matched = false;
+                        break;
+                    }
+                }
+
+                if (matched) {
+                    if (wordPos + currentInfo.mCharacters.length == wordLen) {
+                        // the word exists in the dictionary.
+                        // only update group.
+                        final int newNodeAddress = buffer.limit();
+                        final boolean hasMultipleChars = currentInfo.mCharacters.length > 1;
+                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(hasMultipleChars,
+                                isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
+                                isNotAWord, isBlackListEntry, header.mFormatOptions);
+                        final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
+                                -1 /* endAddress */, flags, currentInfo.mCharacters, frequency,
+                                nodeParentAddress, currentInfo.mChildrenAddress, shortcuts,
+                                bigrams);
+                        moveCharGroup(destination, buffer, newInfo, nodeOriginAddress, address,
+                                header.mFormatOptions);
+                        return;
+                    }
+                    wordPos += currentInfo.mCharacters.length;
+                    if (currentInfo.mChildrenAddress == FormatSpec.NO_CHILDREN_ADDRESS) {
+                        /*
+                         * found the prefix of the word.
+                         * make new node and link to the node from this group.
+                         *
+                         * before
+                         * ab - cd
+                         *
+                         * insert "abcde"
+                         *
+                         * after
+                         * ab - cd - e
+                         */
+                        final int newNodeAddress = buffer.limit();
+                        updateChildrenAddress(buffer, address, newNodeAddress,
+                                header.mFormatOptions);
+                        final int newGroupAddress = newNodeAddress + 1;
+                        final boolean hasMultipleChars = (wordLen - wordPos) > 1;
+                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(hasMultipleChars,
+                                isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
+                                isNotAWord, isBlackListEntry, header.mFormatOptions);
+                        final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
+                        final CharGroupInfo newInfo = new CharGroupInfo(newGroupAddress, -1, flags,
+                                characters, frequency, address, FormatSpec.NO_CHILDREN_ADDRESS,
+                                shortcuts, bigrams);
+                        writeNode(destination, new CharGroupInfo[] { newInfo });
+                        return;
+                    }
+                    buffer.position(currentInfo.mChildrenAddress);
+                    foundNextGroup = true;
+                    break;
+                }
+            }
+
+            if (foundNextGroup) continue;
+
+            // reached the end of the array.
+            final int linkAddressPosition = buffer.position();
+            int nextLink = buffer.readUnsignedInt24();
+            if ((nextLink & MSB24) != 0) {
+                nextLink = -(nextLink & SINT24_MAX);
+            }
+            if (nextLink == FormatSpec.NO_FORWARD_LINK_ADDRESS) {
+                /*
+                 * expand this node.
+                 *
+                 * before
+                 * ab - cd
+                 *
+                 * insert "abef"
+                 *
+                 * after
+                 * ab - cd
+                 *    |
+                 *    - ef
+                 */
+
+                // change the forward link address.
+                final int newNodeAddress = buffer.limit();
+                buffer.position(linkAddressPosition);
+                writeSInt24ToBuffer(buffer, newNodeAddress);
+
+                final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
+                final int flags = BinaryDictInputOutput.makeCharGroupFlags(characters.length > 1,
+                        isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
+                        isNotAWord, isBlackListEntry, header.mFormatOptions);
+                final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
+                        -1 /* endAddress */, flags, characters, frequency, nodeParentAddress,
+                        FormatSpec.NO_CHILDREN_ADDRESS, shortcuts, bigrams);
+                writeNode(destination, new CharGroupInfo[]{ newInfo });
+                return;
+            } else {
+                depth--;
+                buffer.position(nextLink);
+            }
+        }
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
index 624e72f..2d39094 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
@@ -411,7 +411,8 @@
      * Helper method to check whether the group is moved.
      */
     public static boolean isMovedGroup(final int flags, final FormatOptions options) {
-        return options.mSupportsDynamicUpdate && ((flags & FormatSpec.FLAG_IS_MOVED) == 1);
+        return options.mSupportsDynamicUpdate
+                && ((flags & FormatSpec.MASK_GROUP_ADDRESS_TYPE) == FormatSpec.FLAG_IS_MOVED);
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java b/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
index 3193ef4..6f1faa1 100644
--- a/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
@@ -279,7 +279,7 @@
     /**
      * Helper method to convert a String to an int array.
      */
-    static private int[] getCodePoints(final String word) {
+    static int[] getCodePoints(final String word) {
         // TODO: this is a copy-paste of the contents of StringUtils.toCodePointArray,
         // which is not visible from the makedict package. Factor this code.
         final char[] characters = word.toCharArray();
diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
new file mode 100644
index 0000000..7607b58
--- /dev/null
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
@@ -0,0 +1,335 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * 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.
+ */
+
+package com.android.inputmethod.latin.makedict;
+
+import com.android.inputmethod.latin.CollectionUtils;
+import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.ByteBufferWrapper;
+import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.CharEncoding;
+import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.FusionDictionaryBufferInterface;
+import com.android.inputmethod.latin.makedict.FormatSpec.FileHeader;
+import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
+import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+
+import android.test.AndroidTestCase;
+import android.test.MoreAsserts;
+import android.util.Log;
+
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.channels.FileChannel;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Random;
+
+public class BinaryDictIOUtilsTests  extends AndroidTestCase{
+    private static final String TAG = BinaryDictIOUtilsTests.class.getSimpleName();
+    private static final FormatSpec.FormatOptions FORMAT_OPTIONS =
+            new FormatSpec.FormatOptions(3, true);
+    private static final int MAX_UNIGRAMS = 1500;
+
+    private static final ArrayList<String> sWords = CollectionUtils.newArrayList();
+
+    private static final String[] CHARACTERS = {
+        "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",
+        "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z",
+        "\u00FC" /* ü */, "\u00E2" /* â */, "\u00F1" /* ñ */, // accented characters
+        "\u4E9C" /* 亜 */, "\u4F0A" /* 伊 */, "\u5B87" /* 宇 */, // kanji
+        "\uD841\uDE28" /* 𠘨 */, "\uD840\uDC0B" /* 𠀋 */, "\uD861\uDeD7" /* 𨛗 */ // surrogate pair
+    };
+
+    public BinaryDictIOUtilsTests() {
+        super();
+        final Random random = new Random(123456);
+        sWords.clear();
+        for (int i = 0; i < MAX_UNIGRAMS; ++i) {
+            sWords.add(generateWord(random.nextInt()));
+        }
+    }
+
+    // Utilities for test
+    private String generateWord(final int value) {
+        final int lengthOfChars = CHARACTERS.length;
+        StringBuilder builder = new StringBuilder("");
+        long lvalue = Math.abs((long)value);
+        while (lvalue > 0) {
+            builder.append(CHARACTERS[(int)(lvalue % lengthOfChars)]);
+            lvalue /= lengthOfChars;
+        }
+        if (builder.toString().equals("")) return "a";
+        return builder.toString();
+    }
+
+    private static void printCharGroup(final CharGroupInfo info) {
+        Log.d(TAG, "    CharGroup at " + info.mOriginalAddress);
+        Log.d(TAG, "        flags = " + info.mFlags);
+        Log.d(TAG, "        parentAddress = " + info.mParentAddress);
+        Log.d(TAG, "        characters = " + new String(info.mCharacters, 0,
+                info.mCharacters.length));
+        if (info.mFrequency != -1) Log.d(TAG, "        frequency = " + info.mFrequency);
+        if (info.mChildrenAddress == FormatSpec.NO_CHILDREN_ADDRESS) {
+            Log.d(TAG, "        children address = no children address");
+        } else {
+            Log.d(TAG, "        children address = " + info.mChildrenAddress);
+        }
+        if (info.mShortcutTargets != null) {
+            for (final WeightedString ws : info.mShortcutTargets) {
+                Log.d(TAG, "        shortcuts = " + ws.mWord);
+            }
+        }
+        if (info.mBigrams != null) {
+            for (final PendingAttribute attr : info.mBigrams) {
+                Log.d(TAG, "        bigram = " + attr.mAddress);
+            }
+        }
+        Log.d(TAG, "    end address = " + info.mEndAddress);
+    }
+
+    private static void printNode(final FusionDictionaryBufferInterface buffer,
+            final FormatSpec.FormatOptions formatOptions) {
+        Log.d(TAG, "Node at " + buffer.position());
+        final int count = BinaryDictInputOutput.readCharGroupCount(buffer);
+        Log.d(TAG, "    charGroupCount = " + count);
+        for (int i = 0; i < count; ++i) {
+            final CharGroupInfo currentInfo = BinaryDictInputOutput.readCharGroup(buffer,
+                    buffer.position(), formatOptions);
+            printCharGroup(currentInfo);
+        }
+        if (formatOptions.mSupportsDynamicUpdate) {
+            final int forwardLinkAddress = buffer.readUnsignedInt24();
+            Log.d(TAG, "    forwardLinkAddress = " + forwardLinkAddress);
+        }
+    }
+
+    private static void printBinaryFile(final FusionDictionaryBufferInterface buffer)
+            throws IOException, UnsupportedFormatException {
+        FileHeader header = BinaryDictInputOutput.readHeader(buffer);
+        while (buffer.position() < buffer.limit()) {
+            printNode(buffer, header.mFormatOptions);
+        }
+    }
+
+    private int getWordPosition(final File file, final String word) {
+        int position = FormatSpec.NOT_VALID_WORD;
+        FileInputStream inStream = null;
+        try {
+            inStream = new FileInputStream(file);
+            final FusionDictionaryBufferInterface buffer = new ByteBufferWrapper(
+                    inStream.getChannel().map(FileChannel.MapMode.READ_ONLY, 0, file.length()));
+            position = BinaryDictIOUtils.getTerminalPosition(buffer, word);
+        } catch (IOException e) {
+        } catch (UnsupportedFormatException e) {
+        } finally {
+            if (inStream != null) {
+                try {
+                    inStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
+        return position;
+    }
+
+    // return amount of time to insert a word
+    private long insertAndCheckWord(final File file, final String word, final int frequency,
+            final boolean exist) {
+        RandomAccessFile raFile = null;
+        FileOutputStream outStream = null;
+        FusionDictionaryBufferInterface buffer = null;
+        long amountOfTime = -1;
+        try {
+            raFile = new RandomAccessFile(file, "rw");
+            buffer = new ByteBufferWrapper(raFile.getChannel().map(
+                    FileChannel.MapMode.READ_WRITE, 0, file.length()));
+            outStream = new FileOutputStream(file, true);
+
+            if (!exist) {
+                assertEquals(FormatSpec.NOT_VALID_WORD, getWordPosition(file, word));
+            }
+            final long now = System.nanoTime();
+            BinaryDictIOUtils.insertWord(buffer, outStream, word, frequency, null, null, false,
+                    false);
+            amountOfTime = System.nanoTime() - now;
+            MoreAsserts.assertNotEqual(FormatSpec.NOT_VALID_WORD, getWordPosition(file, word));
+            outStream.close();
+            raFile.close();
+        } catch (IOException e) {
+        } catch (UnsupportedFormatException e) {
+        } finally {
+            if (outStream != null) {
+                try {
+                    outStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+            if (raFile != null) {
+                try {
+                    raFile.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
+        return amountOfTime;
+    }
+
+    private void deleteWord(final File file, final String word) {
+        RandomAccessFile raFile = null;
+        FusionDictionaryBufferInterface buffer = null;
+        try {
+            raFile = new RandomAccessFile(file, "rw");
+            buffer = new ByteBufferWrapper(raFile.getChannel().map(
+                    FileChannel.MapMode.READ_WRITE, 0, file.length()));
+            BinaryDictIOUtils.deleteWord(buffer, word);
+        } catch (IOException e) {
+        } catch (UnsupportedFormatException e) {
+        } finally {
+            if (raFile != null) {
+                try {
+                    raFile.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
+    }
+
+
+
+    private void checkReverseLookup(final File file, final String word, final int position) {
+        FileInputStream inStream = null;
+        try {
+            inStream = new FileInputStream(file);
+            final FusionDictionaryBufferInterface buffer = new ByteBufferWrapper(
+                    inStream.getChannel().map(FileChannel.MapMode.READ_ONLY, 0, file.length()));
+            final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
+            assertEquals(word, BinaryDictInputOutput.getWordAtAddress(buffer, header.mHeaderSize,
+                    position - header.mHeaderSize, header.mFormatOptions));
+        } catch (IOException e) {
+        } catch (UnsupportedFormatException e) {
+        } finally {
+            if (inStream != null) {
+                try {
+                    inStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
+    }
+
+    public void testInsertWord() {
+        File file = null;
+        try {
+            file = File.createTempFile("testInsertWord", ".dict");
+        } catch (IOException e) {
+            fail("IOException while creating temporary file: " + e);
+        }
+
+        // set an initial dictionary.
+        final FusionDictionary dict = new FusionDictionary(new Node(),
+                new FusionDictionary.DictionaryOptions(new HashMap<String,String>(), false, false));
+        dict.add("abcd", 10, null, false);
+
+        try {
+            final FileOutputStream out = new FileOutputStream(file);
+            BinaryDictInputOutput.writeDictionaryBinary(out, dict, FORMAT_OPTIONS);
+            out.close();
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        } catch (UnsupportedFormatException e) {
+            fail("UnsupportedFormatException while writing an initial dictionary : " + e);
+        }
+
+        MoreAsserts.assertNotEqual(FormatSpec.NOT_VALID_WORD, getWordPosition(file, "abcd"));
+        insertAndCheckWord(file, "abcde", 10, false);
+
+        insertAndCheckWord(file, "abcdefghijklmn", 10, false);
+        checkReverseLookup(file, "abcdefghijklmn", getWordPosition(file, "abcdefghijklmn"));
+
+        insertAndCheckWord(file, "abcdabcd", 10, false);
+        checkReverseLookup(file, "abcdabcd", getWordPosition(file, "abcdabcd"));
+
+        // update the existing word.
+        insertAndCheckWord(file, "abcdabcd", 15, true);
+
+        // split 1
+        insertAndCheckWord(file, "ab", 20, false);
+
+        // split 2
+        insertAndCheckWord(file, "ami", 30, false);
+
+        deleteWord(file, "ami");
+        assertEquals(FormatSpec.NOT_VALID_WORD, getWordPosition(file, "ami"));
+
+        insertAndCheckWord(file, "abcdabfg", 30, false);
+
+        deleteWord(file, "abcd");
+        assertEquals(FormatSpec.NOT_VALID_WORD, getWordPosition(file, "abcd"));
+    }
+
+    public void testRandomWords() {
+        File file = null;
+        try {
+            file = File.createTempFile("testRandomWord", ".dict");
+        } catch (IOException e) {
+        }
+        assertNotNull(file);
+
+        // set an initial dictionary.
+        final FusionDictionary dict = new FusionDictionary(new Node(),
+                new FusionDictionary.DictionaryOptions(new HashMap<String, String>(), false,
+                        false));
+        dict.add("initial", 10, null, false);
+
+        try {
+            final FileOutputStream out = new FileOutputStream(file);
+            BinaryDictInputOutput.writeDictionaryBinary(out, dict, FORMAT_OPTIONS);
+            out.close();
+        } catch (IOException e) {
+            assertTrue(false);
+        } catch (UnsupportedFormatException e) {
+            assertTrue(false);
+        }
+
+        long maxTimeToInsert = 0, sum = 0;
+        long minTimeToInsert = 100000000; // 1000000000 is an upper bound for minTimeToInsert.
+        int cnt = 0;
+        for (final String word : sWords) {
+            final long diff = insertAndCheckWord(file, word, cnt%255, false);
+            maxTimeToInsert = Math.max(maxTimeToInsert, diff);
+            minTimeToInsert = Math.min(minTimeToInsert, diff);
+            sum += diff;
+            cnt++;
+        }
+        cnt = 0;
+        for (final String word : sWords) {
+            MoreAsserts.assertNotEqual(FormatSpec.NOT_VALID_WORD, getWordPosition(file, word));
+        }
+
+        Log.d(TAG, "max = " + ((double)maxTimeToInsert/1000000) + " ms.");
+        Log.d(TAG, "min = " + ((double)minTimeToInsert/1000000) + " ms.");
+        Log.d(TAG, "avg = " + ((double)sum/MAX_UNIGRAMS/1000000) + " ms.");
+    }
+}