title: Is there a way to make mock functions "interesting" with ON_CALL?
body: <p>Given:</p>
  
  <pre><code>#include "gmock/gmock.h"
  #include &lt;string&gt;
  
  using namespace testing; // tsk, tsk
  
  // -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  
  struct Mockable {
      virtual std::string ify(int x) const;
  };
  
  std::string Mockable::ify(int x) const
  {
      return std::to_string(x);
  }
  
  // -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  
  struct Mocked : public Mockable {
      MOCK_CONST_METHOD1(ify, std::string(int));
  };
  
  // -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  
  std::string tested(Mockable const&amp; u, int x)
  {
      return u.ify(x);
  }
  
  TEST(TC,T42)
  {
      Mocked mock;
      ON_CALL(mock, ify(Eq(42)))
      .WillByDefault(Return("33"));
  
      std::string const&amp; ret = tested(mock, 42);
      EXPECT_EQ("42", ret);
  }
  
  TEST(TC,T33)
  {
      Mocked mock;
      ON_CALL(mock, ify(Eq(33)))
      .WillByDefault(Return("333"));
  
      std::string const&amp; ret = tested(mock, 42);
      EXPECT_EQ("42", ret);
  }
  
  int main(int argc, char *argv[])
  {
      ::testing::InitGoogleTest(&amp;argc, argv);
      //::testing::FLAGS_gmock_verbose = "info";
  
      return RUN_ALL_TESTS();
  }
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>$ ./mocktest 
  [==========] Running 2 tests from 1 test case.
  [----------] Global test environment set-up.
  [----------] 2 tests from TC
  [ RUN      ] TC.T42
  
  GMOCK WARNING:
  Uninteresting mock function call - taking default action specified at:
  mocktest.cc:40:
      Function call: ify(42)
            Returns: "33"
  Stack trace:
  mocktest.cc:44: Failure
  Value of: ret
    Actual: "33"
  Expected: "42"
  [  FAILED  ] TC.T42 (0 ms)
  [ RUN      ] TC.T33
  
  GMOCK WARNING:
  Uninteresting mock function call - returning default value.
      Function call: ify(42)
            Returns: ""
  Stack trace:
  mocktest.cc:54: Failure
  Value of: ret
    Actual: ""
  Expected: "42"
  [  FAILED  ] TC.T33 (1 ms)
  [----------] 2 tests from TC (1 ms total)
  
  [----------] Global test environment tear-down
  [==========] 2 tests from 1 test case ran. (1 ms total)
  [  PASSED  ] 0 tests.
  [  FAILED  ] 2 tests, listed below:
  [  FAILED  ] TC.T42
  [  FAILED  ] TC.T33
  </code></pre>
  
  <p>In both cases, Gmock behaves correctly w.r.t. applying the behavior (or not, in TC33). But why does it say "Uninteresting mock function call" in both cases? Are mock function calls interesting only when specified with <code>EXPECT_CALL</code> ?</p>