Index: unittests/Utility/CMakeLists.txt
===================================================================
--- unittests/Utility/CMakeLists.txt
+++ unittests/Utility/CMakeLists.txt
@@ -16,6 +16,7 @@
   StreamTeeTest.cpp
   StreamTest.cpp
   StringExtractorTest.cpp
+  StringLexerTest.cpp
   StringListTest.cpp
   StructuredDataTest.cpp
   TildeExpressionResolverTest.cpp
Index: unittests/Utility/StringLexerTest.cpp
===================================================================
--- /dev/null
+++ unittests/Utility/StringLexerTest.cpp
@@ -0,0 +1,141 @@
+//===-- StringLexerTest.cpp -------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/Utility/StringLexer.h"
+#include "gtest/gtest.h"
+
+using namespace lldb_utility;
+
+TEST(StringLexerTest, GetUnlexed) {
+  StringLexer l("foo");
+  EXPECT_EQ("foo", l.GetUnlexed());
+  l.Next();
+  EXPECT_EQ("oo", l.GetUnlexed());
+  l.Next();
+  l.Next();
+  EXPECT_EQ("", l.GetUnlexed());
+}
+
+TEST(StringLexerTest, HasAtLeast) {
+  StringLexer l("foo");
+  EXPECT_FALSE(l.HasAtLeast(5));
+  EXPECT_FALSE(l.HasAtLeast(4));
+  EXPECT_TRUE(l.HasAtLeast(3));
+  EXPECT_TRUE(l.HasAtLeast(2));
+  EXPECT_TRUE(l.HasAtLeast(1));
+
+  l.Next();
+  EXPECT_FALSE(l.HasAtLeast(5));
+  EXPECT_FALSE(l.HasAtLeast(4));
+  EXPECT_FALSE(l.HasAtLeast(3));
+  EXPECT_TRUE(l.HasAtLeast(2));
+  EXPECT_TRUE(l.HasAtLeast(1));
+
+  l.Next();
+  l.Next();
+  EXPECT_FALSE(l.HasAtLeast(5));
+  EXPECT_FALSE(l.HasAtLeast(4));
+  EXPECT_FALSE(l.HasAtLeast(3));
+  EXPECT_FALSE(l.HasAtLeast(2));
+  EXPECT_FALSE(l.HasAtLeast(1));
+}
+
+TEST(StringLexerTest, AdvanceIf) {
+  StringLexer l("foobar");
+
+  EXPECT_FALSE(l.AdvanceIf("oo"));
+  // Skip the "fo" part.
+  EXPECT_TRUE(l.AdvanceIf("fo"));
+  EXPECT_FALSE(l.AdvanceIf("obarz"));
+  // Skip the remaining string.
+  EXPECT_TRUE(l.AdvanceIf("obar"));
+
+  EXPECT_FALSE(l.AdvanceIf("obarz"));
+  EXPECT_FALSE(l.AdvanceIf("foo"));
+  EXPECT_FALSE(l.AdvanceIf("o"));
+  EXPECT_FALSE(l.AdvanceIf(" "));
+}
+
+TEST(StringLexerTest, PutBack) {
+  StringLexer l("foo");
+
+  l.Next();
+  l.PutBack(1);
+  EXPECT_EQ("foo", l.GetUnlexed());
+
+  l.Next();
+  l.Next();
+  l.Next();
+  l.PutBack(2);
+  EXPECT_EQ("oo", l.GetUnlexed());
+
+  l.PutBack(1);
+  EXPECT_EQ("foo", l.GetUnlexed());
+}
+
+TEST(StringLexerTest, Peek) {
+  StringLexer l("foo");
+
+  EXPECT_EQ('f', l.Peek());
+  l.Next();
+  EXPECT_EQ('o', l.Peek());
+  l.Next();
+  EXPECT_EQ('o', l.Peek());
+}
+
+TEST(StringLexerTest, Next) {
+  StringLexer l("foo");
+  EXPECT_EQ('f', l.Next());
+  EXPECT_EQ('o', l.Next());
+  EXPECT_EQ('o', l.Next());
+}
+
+TEST(StringLexerTest, NextIf) {
+  StringLexer l("foo");
+
+  EXPECT_FALSE(l.NextIf('\0'));
+  EXPECT_FALSE(l.NextIf(' '));
+  EXPECT_FALSE(l.NextIf('o'));
+
+  EXPECT_TRUE(l.NextIf('f'));
+
+  EXPECT_FALSE(l.NextIf('\0'));
+  EXPECT_FALSE(l.NextIf(' '));
+  EXPECT_FALSE(l.NextIf('f'));
+
+  EXPECT_TRUE(l.NextIf('o'));
+
+  EXPECT_FALSE(l.NextIf('\0'));
+  EXPECT_FALSE(l.NextIf(' '));
+  EXPECT_FALSE(l.NextIf('f'));
+
+  EXPECT_TRUE(l.NextIf('o'));
+}
+
+TEST(StringLexerTest, NextIfList) {
+  StringLexer l("foo");
+
+  EXPECT_FALSE(l.NextIf({'\0', ' ', 'o'}).first);
+
+  auto r = l.NextIf({'f'});
+  EXPECT_TRUE(r.first);
+  EXPECT_EQ('f', r.second);
+
+  EXPECT_FALSE(l.NextIf({'\0', ' ', 'f'}).first);
+
+  r = l.NextIf({'f', 'o'});
+  EXPECT_TRUE(r.first);
+  EXPECT_EQ('o', r.second);
+
+  EXPECT_FALSE(l.NextIf({'\0', ' ', 'f'}).first);
+
+  r = l.NextIf({'*', 'f', 'o', 'o'});
+  EXPECT_TRUE(r.first);
+  EXPECT_EQ('o', r.second);
+}