Index: llvm/trunk/lib/Fuzzer/test/CMakeLists.txt
===================================================================
--- llvm/trunk/lib/Fuzzer/test/CMakeLists.txt
+++ llvm/trunk/lib/Fuzzer/test/CMakeLists.txt
@@ -18,6 +18,7 @@
   CallerCalleeTest
   CounterTest
   CustomMutatorTest
+  EmptyTest
   FourIndependentBranchesTest
   FullCoverageSetTest
   InitializeTest
Index: llvm/trunk/lib/Fuzzer/test/EmptyTest.cpp
===================================================================
--- llvm/trunk/lib/Fuzzer/test/EmptyTest.cpp
+++ llvm/trunk/lib/Fuzzer/test/EmptyTest.cpp
@@ -0,0 +1,11 @@
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+// A fuzzer with empty target function.
+
+#include <cstdint>
+#include <cstdlib>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  return 0;
+}
Index: llvm/trunk/lib/Fuzzer/test/FuzzerUnittest.cpp
===================================================================
--- llvm/trunk/lib/Fuzzer/test/FuzzerUnittest.cpp
+++ llvm/trunk/lib/Fuzzer/test/FuzzerUnittest.cpp
@@ -13,10 +13,6 @@
   abort();
 }
 
-static int EmptyLLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
-  return 0;
-}
-
 TEST(Fuzzer, CrossOver) {
   Random Rand(0);
   MutationDispatcher MD(Rand);
@@ -427,21 +423,3 @@
     EXPECT_GT(Hist[i], TriesPerUnit / N / 3);
   }
 }
-
-TEST(Corpus, TruncateUnits) {
-  Random Rand(0);
-  MutationDispatcher MD(Rand);
-  Fuzzer::FuzzingOptions Options;
-  Options.OutputCorpus = ""; // stops from writing new units.
-  Fuzzer Fuzz(EmptyLLVMFuzzerTestOneInput, MD, Options);
-
-  Fuzz.AddToCorpus(Unit(1024, static_cast<uint8_t>(1)));
-  Fuzz.ResetCoverage();
-
-  std::vector<Unit> NewCorpus;
-  Fuzz.TruncateUnits(&NewCorpus);
-
-  // New corpus should have a shorter unit.
-  EXPECT_EQ(1ul, NewCorpus.size());
-  EXPECT_EQ(1ul, NewCorpus[0].size());
-}
Index: llvm/trunk/lib/Fuzzer/test/fuzzer-trunc.test
===================================================================
--- llvm/trunk/lib/Fuzzer/test/fuzzer-trunc.test
+++ llvm/trunk/lib/Fuzzer/test/fuzzer-trunc.test
@@ -0,0 +1,10 @@
+# Test truncate_units option.
+RUN: rm -rf FuzzerTruncateTestCORPUS
+RUN: mkdir FuzzerTruncateTestCORPUS
+RUN: echo "01234567890123456789012345678901234567890" > FuzzerTruncateTestCORPUS/unit1
+# Simply running a fuzzer won't produce new results
+RUN:   LLVMFuzzer-EmptyTest -seed=1 -runs=100 -truncate_units=0 ./FuzzerTruncateTestCORPUS
+# Truncating would create a new unit of length 1.
+RUN:   LLVMFuzzer-EmptyTest -seed=1 -runs=0 -truncate_units=1 ./FuzzerTruncateTestCORPUS
+RUN: find FuzzerTruncateTestCORPUS/b6589fc6ab0dc82cf12099d1c2d40ab994e8410c
+RUN: rm -rf FuzzerTruncateTestCORPUS