Cut main from gen tests

Summary: [Folly] Cut explicit `main` from test programs in `folly/gen/test/` and prefer the linked-in version.

Reviewed By: simpkins

Differential Revision: D23643891

fbshipit-source-id: 20152ae4feeeccd43038580043d45759c39c075c

folly/gen/test/BaseTest.cpp

@@ -1466,9 +1466,3 @@ TEST(Gen, Unwrap) {
     EXPECT_EQ(&x, empty | unwrapOr(&x));
   }
 }
-
-int main(int argc, char* argv[]) {
-  testing::InitGoogleTest(&argc, argv);
-  gflags::ParseCommandLineFlags(&argc, &argv, true);
-  return RUN_ALL_TESTS();
-}

folly/gen/test/CombineTest.cpp

@@ -206,9 +206,3 @@ TEST(CombineGen, TupleFlatten) {
   ASSERT_EQ(zipped6.size(), 3);
   EXPECT_EQ(zipped6[0], std::make_tuple(1, "1", 'A', 1.0));
 }
-
-int main(int argc, char* argv[]) {
-  testing::InitGoogleTest(&argc, argv);
-  gflags::ParseCommandLineFlags(&argc, &argv, true);
-  return RUN_ALL_TESTS();
-}

folly/gen/test/ParallelMapTest.cpp

@@ -158,9 +158,3 @@ TEST(Pmap, Exception) {
   std::vector<char const*> input{"a"};
   EXPECT_THROW(from(input) | pmap(To<int>()) | count, std::runtime_error);
 }
-
-int main(int argc, char* argv[]) {
-  testing::InitGoogleTest(&argc, argv);
-  gflags::ParseCommandLineFlags(&argc, &argv, true);
-  return RUN_ALL_TESTS();
-}

folly/gen/test/ParallelTest.cpp

@@ -104,9 +104,3 @@ TEST(ParallelTest, PSum) {
       from(primes) | map(sleepyWork) | sum,
       from(primes) | parallel(map(sleepyWork) | sub(sum)) | sum);
 }
-
-int main(int argc, char* argv[]) {
-  testing::InitGoogleTest(&argc, argv);
-  gflags::ParseCommandLineFlags(&argc, &argv, true);
-  return RUN_ALL_TESTS();
-}