diff --git a/native/jni/NativeFileList.mk b/native/jni/NativeFileList.mk
index f21b54c..4f77388 100644
--- a/native/jni/NativeFileList.mk
+++ b/native/jni/NativeFileList.mk
@@ -134,5 +134,6 @@
     suggest/policyimpl/dictionary/utils/trie_map_test.cpp \
     suggest/policyimpl/utils/damerau_levenshtein_edit_distance_policy_test.cpp \
     utils/autocorrection_threshold_utils_test.cpp \
+    utils/char_utils_test.cpp \
     utils/int_array_view_test.cpp \
     utils/time_keeper_test.cpp
diff --git a/native/jni/src/utils/char_utils.cpp b/native/jni/src/utils/char_utils.cpp
index b17e084..3bb9055 100644
--- a/native/jni/src/utils/char_utils.cpp
+++ b/native/jni/src/utils/char_utils.cpp
@@ -1057,11 +1057,11 @@
             - static_cast<int>((static_cast<const struct LatinCapitalSmallPair *>(b))->capital);
 }
 
-/* static */ unsigned short CharUtils::latin_tolower(const unsigned short c) {
+/* static */ int CharUtils::latin_tolower(const int c) {
     struct LatinCapitalSmallPair *p =
             static_cast<struct LatinCapitalSmallPair *>(bsearch(&c, SORTED_CHAR_MAP,
                     NELEMS(SORTED_CHAR_MAP), sizeof(SORTED_CHAR_MAP[0]), compare_pair_capital));
-    return p ? p->small : c;
+    return p ? static_cast<int>(p->small) : c;
 }
 
 /*
diff --git a/native/jni/src/utils/char_utils.h b/native/jni/src/utils/char_utils.h
index 6378650..5e9cdd9 100644
--- a/native/jni/src/utils/char_utils.h
+++ b/native/jni/src/utils/char_utils.h
@@ -27,20 +27,14 @@
 
 class CharUtils {
  public:
+    static const std::vector<int> EMPTY_STRING;
+
     static AK_FORCE_INLINE bool isAsciiUpper(int c) {
         // Note: isupper(...) reports false positives for some Cyrillic characters, causing them to
         // be incorrectly lower-cased using toAsciiLower(...) rather than latin_tolower(...).
         return (c >= 'A' && c <= 'Z');
     }
 
-    static AK_FORCE_INLINE int toAsciiLower(int c) {
-        return c - 'A' + 'a';
-    }
-
-    static AK_FORCE_INLINE bool isAscii(int c) {
-        return isascii(c) != 0;
-    }
-
     static AK_FORCE_INLINE int toLowerCase(const int c) {
         if (isAsciiUpper(c)) {
             return toAsciiLower(c);
@@ -48,7 +42,7 @@
         if (isAscii(c)) {
             return c;
         }
-        return static_cast<int>(latin_tolower(static_cast<unsigned short>(c)));
+        return latin_tolower(c);
     }
 
     static AK_FORCE_INLINE int toBaseLowerCase(const int c) {
@@ -59,7 +53,6 @@
         // TODO: Do not hardcode here
         return codePoint == KEYCODE_SINGLE_QUOTE || codePoint == KEYCODE_HYPHEN_MINUS;
     }
-
     static AK_FORCE_INLINE int getCodePointCount(const int arraySize, const int *const codePoints) {
         int size = 0;
         for (; size < arraySize; ++size) {
@@ -91,9 +84,6 @@
         return codePoint >= MIN_UNICODE_CODE_POINT && codePoint <= MAX_UNICODE_CODE_POINT;
     }
 
-    static unsigned short latin_tolower(const unsigned short c);
-    static const std::vector<int> EMPTY_STRING;
-
     // Returns updated code point count. Returns 0 when the code points cannot be marked as a
     // Beginning-of-Sentence.
     static AK_FORCE_INLINE int attachBeginningOfSentenceMarker(int *const codePoints,
@@ -125,6 +115,16 @@
      */
     static const int BASE_CHARS_SIZE = 0x0500;
     static const unsigned short BASE_CHARS[BASE_CHARS_SIZE];
+
+    static AK_FORCE_INLINE bool isAscii(int c) {
+        return isascii(c) != 0;
+    }
+
+    static AK_FORCE_INLINE int toAsciiLower(int c) {
+        return c - 'A' + 'a';
+    }
+
+    static int latin_tolower(const int c);
 };
 } // namespace latinime
 #endif // LATINIME_CHAR_UTILS_H
diff --git a/native/jni/tests/utils/char_utils_test.cpp b/native/jni/tests/utils/char_utils_test.cpp
new file mode 100644
index 0000000..01d5340
--- /dev/null
+++ b/native/jni/tests/utils/char_utils_test.cpp
@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+#include "utils/char_utils.h"
+
+#include <gtest/gtest.h>
+
+#include "defines.h"
+
+namespace latinime {
+namespace {
+
+TEST(CharUtilsTest, TestIsAsciiUpper) {
+    EXPECT_TRUE(CharUtils::isAsciiUpper('A'));
+    EXPECT_TRUE(CharUtils::isAsciiUpper('Z'));
+    EXPECT_FALSE(CharUtils::isAsciiUpper('a'));
+    EXPECT_FALSE(CharUtils::isAsciiUpper('z'));
+    EXPECT_FALSE(CharUtils::isAsciiUpper('@'));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(' '));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(0x00C0 /* LATIN CAPITAL LETTER A WITH GRAVE */));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(0x00E0 /* LATIN SMALL LETTER A WITH GRAVE */));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(0x03C2 /* GREEK SMALL LETTER FINAL SIGMA */));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(0x0410 /* CYRILLIC CAPITAL LETTER A */));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(0x0430 /* CYRILLIC SMALL LETTER A */));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(0x3042 /* HIRAGANA LETTER A */));
+    EXPECT_FALSE(CharUtils::isAsciiUpper(0x1F36A /* COOKIE */));
+}
+
+TEST(CharUtilsTest, TestToLowerCase) {
+    EXPECT_EQ('a', CharUtils::toLowerCase('A'));
+    EXPECT_EQ('z', CharUtils::toLowerCase('Z'));
+    EXPECT_EQ('a', CharUtils::toLowerCase('a'));
+    EXPECT_EQ('z', CharUtils::toLowerCase('z'));
+    EXPECT_EQ('@', CharUtils::toLowerCase('@'));
+    EXPECT_EQ(' ', CharUtils::toLowerCase(' '));
+    EXPECT_EQ(0x00E0 /* LATIN SMALL LETTER A WITH GRAVE */,
+            CharUtils::toLowerCase(0x00C0 /* LATIN CAPITAL LETTER A WITH GRAVE */));
+    EXPECT_EQ(0x00E0 /* LATIN SMALL LETTER A WITH GRAVE */,
+            CharUtils::toLowerCase(0x00E0 /* LATIN SMALL LETTER A WITH GRAVE */));
+    EXPECT_EQ(0x03C2 /* GREEK SMALL LETTER FINAL SIGMA */,
+            CharUtils::toLowerCase(0x03C2 /* GREEK SMALL LETTER FINAL SIGMA */));
+    EXPECT_EQ(0x0430 /* CYRILLIC SMALL LETTER A */,
+            CharUtils::toLowerCase(0x0410 /* CYRILLIC CAPITAL LETTER A */));
+    EXPECT_EQ(0x0430 /* CYRILLIC SMALL LETTER A */,
+            CharUtils::toLowerCase(0x0430 /* CYRILLIC SMALL LETTER A */));
+    EXPECT_EQ(0x3042 /* HIRAGANA LETTER A */,
+            CharUtils::toLowerCase(0x3042 /* HIRAGANA LETTER A */));
+    EXPECT_EQ(0x1F36A /* COOKIE */, CharUtils::toLowerCase(0x1F36A /* COOKIE */));
+}
+
+TEST(CharUtilsTest, TestToBaseLowerCase) {
+    EXPECT_EQ('a', CharUtils::toBaseLowerCase('A'));
+    EXPECT_EQ('z', CharUtils::toBaseLowerCase('Z'));
+    EXPECT_EQ('a', CharUtils::toBaseLowerCase('a'));
+    EXPECT_EQ('z', CharUtils::toBaseLowerCase('z'));
+    EXPECT_EQ('@', CharUtils::toBaseLowerCase('@'));
+    EXPECT_EQ(' ', CharUtils::toBaseLowerCase(' '));
+    EXPECT_EQ('a', CharUtils::toBaseLowerCase(0x00C0 /* LATIN CAPITAL LETTER A WITH GRAVE */));
+    EXPECT_EQ('a', CharUtils::toBaseLowerCase(0x00E0 /* LATIN SMALL LETTER A WITH GRAVE */));
+    EXPECT_EQ(0x03C2 /* GREEK SMALL LETTER FINAL SIGMA */,
+            CharUtils::toBaseLowerCase(0x03C2 /* GREEK SMALL LETTER FINAL SIGMA */));
+    EXPECT_EQ(0x0430 /* CYRILLIC SMALL LETTER A */,
+            CharUtils::toBaseLowerCase(0x0410 /* CYRILLIC CAPITAL LETTER A */));
+    EXPECT_EQ(0x0430 /* CYRILLIC SMALL LETTER A */,
+            CharUtils::toBaseLowerCase(0x0430 /* CYRILLIC SMALL LETTER A */));
+    EXPECT_EQ(0x3042 /* HIRAGANA LETTER A */,
+            CharUtils::toBaseLowerCase(0x3042 /* HIRAGANA LETTER A */));
+    EXPECT_EQ(0x1F36A /* COOKIE */, CharUtils::toBaseLowerCase(0x1F36A /* COOKIE */));
+}
+
+TEST(CharUtilsTest, TestToBaseCodePoint) {
+    EXPECT_EQ('A', CharUtils::toBaseCodePoint('A'));
+    EXPECT_EQ('Z', CharUtils::toBaseCodePoint('Z'));
+    EXPECT_EQ('a', CharUtils::toBaseCodePoint('a'));
+    EXPECT_EQ('z', CharUtils::toBaseCodePoint('z'));
+    EXPECT_EQ('@', CharUtils::toBaseCodePoint('@'));
+    EXPECT_EQ(' ', CharUtils::toBaseCodePoint(' '));
+    EXPECT_EQ('A', CharUtils::toBaseCodePoint(0x00C0 /* LATIN CAPITAL LETTER A WITH GRAVE */));
+    EXPECT_EQ('a', CharUtils::toBaseCodePoint(0x00E0 /* LATIN SMALL LETTER A WITH GRAVE */));
+    EXPECT_EQ(0x03C2 /* GREEK SMALL LETTER FINAL SIGMA */,
+            CharUtils::toBaseLowerCase(0x03C2 /* GREEK SMALL LETTER FINAL SIGMA */));
+    EXPECT_EQ(0x0410 /* CYRILLIC CAPITAL LETTER A */,
+            CharUtils::toBaseCodePoint(0x0410 /* CYRILLIC CAPITAL LETTER A */));
+    EXPECT_EQ(0x0430 /* CYRILLIC SMALL LETTER A */,
+            CharUtils::toBaseCodePoint(0x0430 /* CYRILLIC SMALL LETTER A */));
+    EXPECT_EQ(0x3042 /* HIRAGANA LETTER A */,
+            CharUtils::toBaseCodePoint(0x3042 /* HIRAGANA LETTER A */));
+    EXPECT_EQ(0x1F36A /* COOKIE */, CharUtils::toBaseCodePoint(0x1F36A /* COOKIE */));
+}
+
+TEST(CharUtilsTest, TestIsIntentionalOmissionCodePoint) {
+    EXPECT_TRUE(CharUtils::isIntentionalOmissionCodePoint('\''));
+    EXPECT_TRUE(CharUtils::isIntentionalOmissionCodePoint('-'));
+    EXPECT_FALSE(CharUtils::isIntentionalOmissionCodePoint('a'));
+    EXPECT_FALSE(CharUtils::isIntentionalOmissionCodePoint('?'));
+    EXPECT_FALSE(CharUtils::isIntentionalOmissionCodePoint('/'));
+}
+
+TEST(CharUtilsTest, TestIsInUnicodeSpace) {
+    EXPECT_FALSE(CharUtils::isInUnicodeSpace(NOT_A_CODE_POINT));
+    EXPECT_FALSE(CharUtils::isInUnicodeSpace(CODE_POINT_BEGINNING_OF_SENTENCE));
+    EXPECT_TRUE(CharUtils::isInUnicodeSpace('a'));
+    EXPECT_TRUE(CharUtils::isInUnicodeSpace(0x0410 /* CYRILLIC CAPITAL LETTER A */));
+    EXPECT_TRUE(CharUtils::isInUnicodeSpace(0x3042 /* HIRAGANA LETTER A */));
+    EXPECT_TRUE(CharUtils::isInUnicodeSpace(0x1F36A /* COOKIE */));
+}
+
+}  // namespace
+}  // namespace latinime