Implementing erase/erase_if functions from library fundamentals ts:

base/containers/flat_set_unittest.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/containers/flat_set.h"
 
 // Following tests are ported and extended tests from libcpp for std::set.
 // They can be found here:
 // https://github.com/llvm-mirror/libcxx/tree/master/test/std/containers/associative/set
 //
@@ skipping 1224 matching lines @@
 
   EXPECT_EQ(biggest, biggest);
   EXPECT_NE(biggest, smallest);
   EXPECT_LT(smallest, middle);
   EXPECT_LE(smallest, middle);
   EXPECT_LE(middle, middle);
   EXPECT_GT(biggest, middle);
   EXPECT_GE(biggest, middle);
   EXPECT_GE(biggest, biggest);
 }
+
+TEST(FlatSet, EraseIf) {
+  IntSet x;
+  base::EraseIf(x, [](int) { return false; });
+  EXPECT_THAT(x, ElementsAre());
+
+  x = {1, 2, 3};
+  base::EraseIf(x, [](int elem) { return !(elem & 1); });
+  EXPECT_THAT(x, ElementsAre(1, 3));
+
+  x = {1, 2, 3, 4};
+  base::EraseIf(x, [](int elem) { return elem & 1; });
+  EXPECT_THAT(x, ElementsAre(2, 4));
+}