Index: libc/test/CMakeLists.txt
===================================================================
--- libc/test/CMakeLists.txt
+++ libc/test/CMakeLists.txt
@@ -2,3 +2,7 @@
 
 add_subdirectory(config)
 add_subdirectory(src)
+
+if (LIBC_LIT_TESTS)
+  add_subdirectory(test)
+endif()
Index: libc/test/test/CMakeLists.txt
===================================================================
--- /dev/null
+++ libc/test/test/CMakeLists.txt
@@ -0,0 +1,20 @@
+configure_lit_site_cfg(
+  ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in
+  ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py
+  MAIN_CONFIG
+    ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.py
+)
+
+
+set(LLVM_TEST_DEPENDS
+  not
+  FileCheck
+)
+
+add_lit_testsuite(check-libc-lit "Running llvm libc lit tests"
+  ${CMAKE_CURRENT_BINARY_DIR}
+  DEPENDS
+    llvmlibc
+)
+
+set_target_properties(check-libc-lit PROPERTIES FOLDER "Tests")
Index: libc/test/test/lit.cfg.py
===================================================================
--- /dev/null
+++ libc/test/test/lit.cfg.py
@@ -0,0 +1,50 @@
+# -*- Python -*-
+
+import os
+import platform
+import re
+import subprocess
+import tempfile
+
+import lit.formats
+import lit.util
+
+from lit.llvm import llvm_config
+from lit.llvm.subst import ToolSubst
+from lit.llvm.subst import FindTool
+
+# Configuration file for the 'lit' test runner.
+
+# name: The name of this test suite.
+config.name = 'libc'
+
+# testFormat: The test format to use to interpret tests.
+#
+# For now we require '&&' between commands, until they get globally killed and
+# the test runner updated.
+config.test_format = lit.formats.ShTest(not llvm_config.use_lit_shell)
+
+# suffixes: A list of file extensions to treat as test files.
+config.suffixes = ['.c', '.cpp', '.test', '.s']
+
+# excludes: A list of directories to exclude from the testsuite. The 'Inputs'
+# subdirectories contain auxiliary inputs for various tests in their parent
+# directories.
+config.excludes = ['CMakeLists.txt']
+
+# test_source_root: The root path where tests are located.
+config.test_source_root = os.path.dirname(__file__)
+
+llvm_config.use_default_substitutions()
+
+def findLibcIncDir():
+    return config.libc_build_dir + '/include/'
+
+def findLibcDotA():
+    return config.libc_build_dir + '/lib/libllvmlibc.a'
+
+# TODO: in the future when we provide the crt, make sure we aren't linking
+# against the system libc at all.
+config.substitutions.append(
+    ('%clang_libc', 'clang -nostdinc -isystem '
+        + findLibcIncDir() + ' ' + findLibcDotA()))
Index: libc/test/test/lit.site.cfg.py.in
===================================================================
--- /dev/null
+++ libc/test/test/lit.site.cfg.py.in
@@ -0,0 +1,24 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+import sys
+
+config.lit_tools_dir = "@LLVM_LIT_TOOLS_DIR@"
+config.llvm_src_root = "@LLVM_SOURCE_DIR@"
+config.llvm_obj_root = "@LLVM_BINARY_DIR@"
+config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
+config.libc_build_dir = "@LIBC_BUILD_DIR@"
+
+# Support substitution of the tools_dir with user parameters.
+# This is used when we can't determine the tool dir at configuration time.
+try:
+    config.llvm_tools_dir = config.llvm_tools_dir % lit_config.params
+except KeyError:
+    e = sys.exc_info()[1]
+    key, = e.args
+    lit_config.fatal("unable to find %r parameter, use '--param=%s=VALUE'" % (key,key))
+
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
+# Let the main config do the real work.
+lit_config.load_config(config, "@LIBC_SOURCE_DIR@/test/test/lit.cfg.py")
Index: libc/test/test/sanity/includes.c
===================================================================
--- /dev/null
+++ libc/test/test/sanity/includes.c
@@ -0,0 +1,18 @@
+// This tests that all of the expected includes are available in their expected
+// directories and are syntactically valid.
+
+// RUN: %clang_libc %s -fsyntax-only
+
+#include <assert.h>
+// #include <ctype.h> This fails because ctype.h is never copied into the
+// build's include directory.
+#include <errno.h>
+#include <math.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifndef WIN32
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#endif
Index: libc/test/test/sanity/sanity.c
===================================================================
--- /dev/null
+++ libc/test/test/sanity/sanity.c
@@ -0,0 +1,9 @@
+// This is a sanity check to ensure llvm libc headers are in our include path
+// and that the llvm libc lit tests are set up correctly.
+
+// RUN: %clang_libc %s -fsyntax-only 2>&1 | FileCheck %s
+// CHECK: sanity check compiled successfully
+
+#include <__llvm-libc-common.h>
+
+#warning "sanity check compiled successfully"
Index: libc/test/test/src/assert/assert.c
===================================================================
--- /dev/null
+++ libc/test/test/src/assert/assert.c
@@ -0,0 +1,15 @@
+// This tests that asserts error message is as we expect.
+
+// RUN: %clang_libc %s -o %t
+// RUN: not %t | FileCheck %s
+
+// RUN: %clang_libc %s -o %t -DNDEBUG
+// RUN: %t
+
+// CHECK: assert.c: Assertion failed '0' in function 'int main()'
+
+#include <assert.h>
+
+int main() {
+  assert(0);
+}