fix tests for platforms with small std::string

Summary:
F14MapTest's continuousCapacitySmall test implicitly assumed
that folly::F14FastMap<std::size_t, std::string> uses the vector storage
policy, but this is not the case if std::string is 8 bytes.  Remove the
assumption.

Differential Revision: D19431446

fbshipit-source-id: 6e6f0cbe7f57b23b2df38c87bb36a6532ab97a14

folly/container/test/F14MapTest.cpp

@@ -1873,14 +1873,22 @@ void runContinuousCapacityTest(std::size_t minSize, std::size_t maxSize) {
   }
 }
 
-TEST(F14Map, continuousCapacitySmall) {
+TEST(F14Map, continuousCapacitySmall0) {
   runContinuousCapacityTest<folly::F14NodeMap<std::size_t, std::string>>(1, 14);
+}
+
+TEST(F14Map, continuousCapacitySmall1) {
   runContinuousCapacityTest<folly::F14ValueMap<std::size_t, std::string>>(
       1, 14);
+}
+
+TEST(F14Map, continuousCapacitySmall2) {
   runContinuousCapacityTest<folly::F14VectorMap<std::size_t, std::string>>(
       1, 100);
-  runContinuousCapacityTest<folly::F14FastMap<std::size_t, std::string>>(
-      1, 100);
+}
+
+TEST(F14Map, continuousCapacitySmall3) {
+  runContinuousCapacityTest<folly::F14FastMap<std::size_t, std::string>>(1, 14);
 }
 
 TEST(F14Map, continuousCapacityBig0) {