Index: lib/Fuzzer/CMakeLists.txt
===================================================================
--- lib/Fuzzer/CMakeLists.txt
+++ lib/Fuzzer/CMakeLists.txt
@@ -1,15 +1,17 @@
 # Disable the coverage instrumentation for the fuzzer itself.
 set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O2 -fsanitize-coverage=0")
 if( LLVM_USE_SANITIZE_COVERAGE  )
-  add_library(LLVMFuzzer STATIC
-    EXCLUDE_FROM_ALL  # Do not build if you are not building fuzzers.
+  add_library(LLVMFuzzerNoMain OBJECT
     FuzzerCrossOver.cpp
     FuzzerIO.cpp
     FuzzerLoop.cpp
-    FuzzerMain.cpp
     FuzzerMutate.cpp
     FuzzerUtil.cpp
     )
+  add_library(LLVMFuzzer STATIC
+    FuzzerMain.cpp
+    $<TARGET_OBJECTS:LLVMFuzzerNoMain>
+    )
 
   if( LLVM_INCLUDE_TESTS )
     add_subdirectory(test)
Index: lib/Fuzzer/test/CMakeLists.txt
===================================================================
--- lib/Fuzzer/test/CMakeLists.txt
+++ lib/Fuzzer/test/CMakeLists.txt
@@ -25,19 +25,34 @@
   set(TestBinaries ${TestBinaries} LLVMFuzzer-${Test})
 endforeach()
 
-set_target_properties(${TestBinaries}
+configure_lit_site_cfg(
+  ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
+  ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg
+  )
+
+configure_lit_site_cfg(
+  ${CMAKE_CURRENT_SOURCE_DIR}/unit/lit.site.cfg.in
+  ${CMAKE_CURRENT_BINARY_DIR}/unit/lit.site.cfg
+  )
+
+include_directories(..)
+include_directories(${LLVM_MAIN_SRC_DIR}/utils/unittest/googletest/include)
+
+add_executable(LLVMFuzzer-Unittest
+  FuzzerUnittest.cpp
+  $<TARGET_OBJECTS:LLVMFuzzerNoMain>
+  )
+
+target_link_libraries(LLVMFuzzer-Unittest
+  gtest
+  gtest_main
+  )
+
+set_target_properties(${TestBinaries} LLVMFuzzer-Unittest
   PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
   )
 
-set(EXCLUDE_FROM_ALL TRUE)
 add_lit_testsuite(check-fuzzer "Running Fuzzer tests"
     ${CMAKE_CURRENT_BINARY_DIR}
-    DEPENDS ${TestBinaries}
+    DEPENDS ${TestBinaries} LLVMFuzzer-Unittest
     )
-set(EXCLUDE_FROM_ALL FALSE)
-
-configure_lit_site_cfg(
-  ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
-  ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg
-  )
-
Index: lib/Fuzzer/test/FuzzerUnittest.cpp
===================================================================
--- lib/Fuzzer/test/FuzzerUnittest.cpp
+++ lib/Fuzzer/test/FuzzerUnittest.cpp
@@ -1,13 +1,64 @@
 #include "FuzzerInternal.h"
+#include "gtest/gtest.h"
+#include <set>
 
-int main() {
+// Just to make it link.
+extern "C" void TestOneInput(const uint8_t *Data, size_t Size) {
+  abort();
+}
+
+TEST(Fuzzer, CrossOver) {
   using namespace fuzzer;
-  Unit A({0, 1, 2, 3, 4}), B({5, 6, 7, 8, 9});
+  Unit A({0, 1, 2}), B({5, 6, 7});
   Unit C;
-  for (size_t Len = 1; Len < 15; Len++) {
-    for (int Iter = 0; Iter < 1000; Iter++) {
+  Unit Expected[] = {
+       { 0 },
+       { 0, 1 },
+       { 0, 5 },
+       { 0, 1, 2 },
+       { 0, 1, 5 },
+       { 0, 5, 1 },
+       { 0, 5, 6 },
+       { 0, 1, 2, 5 },
+       { 0, 1, 5, 2 },
+       { 0, 1, 5, 6 },
+       { 0, 5, 1, 2 },
+       { 0, 5, 1, 6 },
+       { 0, 5, 6, 1 },
+       { 0, 5, 6, 7 },
+       { 0, 1, 2, 5, 6 },
+       { 0, 1, 5, 2, 6 },
+       { 0, 1, 5, 6, 2 },
+       { 0, 1, 5, 6, 7 },
+       { 0, 5, 1, 2, 6 },
+       { 0, 5, 1, 6, 2 },
+       { 0, 5, 1, 6, 7 },
+       { 0, 5, 6, 1, 2 },
+       { 0, 5, 6, 1, 7 },
+       { 0, 5, 6, 7, 1 },
+       { 0, 1, 2, 5, 6, 7 },
+       { 0, 1, 5, 2, 6, 7 },
+       { 0, 1, 5, 6, 2, 7 },
+       { 0, 1, 5, 6, 7, 2 },
+       { 0, 5, 1, 2, 6, 7 },
+       { 0, 5, 1, 6, 2, 7 },
+       { 0, 5, 1, 6, 7, 2 },
+       { 0, 5, 6, 1, 2, 7 },
+       { 0, 5, 6, 1, 7, 2 },
+       { 0, 5, 6, 7, 1, 2 }
+  };
+  for (size_t Len = 1; Len < 8; Len++) {
+    std::set<Unit> FoundUnits, ExpectedUnitsWitThisLength;
+    for (int Iter = 0; Iter < 3000; Iter++) {
       CrossOver(A, B, &C, Len);
-      Print(C);
+      FoundUnits.insert(C);
+      // Print(C, "\n");
     }
+    for (const Unit &U : Expected)
+      if (U.size() <= Len)
+        ExpectedUnitsWitThisLength.insert(U);
+    // std::cerr << "XXX " << FoundUnits.size() << " "
+    //          << ExpectedUnitsWitThisLength.size() << "\n";
+    EXPECT_EQ(ExpectedUnitsWitThisLength, FoundUnits);
   }
 }
Index: lib/Fuzzer/test/TestFuzzerCrossOver.cpp
===================================================================
--- lib/Fuzzer/test/TestFuzzerCrossOver.cpp
+++ lib/Fuzzer/test/TestFuzzerCrossOver.cpp
@@ -1,13 +0,0 @@
-#include "FuzzerInternal.h"
-
-int main() {
-  using namespace fuzzer;
-  Unit A({0, 1, 2, 3, 4}), B({5, 6, 7, 8, 9});
-  Unit C;
-  for (size_t Len = 1; Len < 15; Len++) {
-    for (int Iter = 0; Iter < 1000; Iter++) {
-      CrossOver(A, B, &C, Len);
-      Print(C);
-    }
-  }
-}
Index: lib/Fuzzer/test/unit/lit.cfg
===================================================================
--- /dev/null
+++ lib/Fuzzer/test/unit/lit.cfg
@@ -0,0 +1,7 @@
+import lit.formats
+
+config.name = "LLVMFuzzer-Unittest"
+print config.test_exec_root
+config.test_format = lit.formats.GoogleTest(".", "Unittest")
+config.suffixes = []
+config.test_source_root = config.test_exec_root
Index: lib/Fuzzer/test/unit/lit.site.cfg.in
===================================================================
--- /dev/null
+++ lib/Fuzzer/test/unit/lit.site.cfg.in
@@ -0,0 +1,2 @@
+config.test_exec_root = "@CMAKE_CURRENT_BINARY_DIR@"
+lit_config.load_config(config, "@CMAKE_CURRENT_SOURCE_DIR@/unit/lit.cfg")