Unit test nullptr C-style strings

Added unit tests for the cases of matching and serializing C-style strings (char*) that are nullptr.

(As of this revision, these new tests correctly fail, except for the test of mock::equal; fix to follow.)

test/test_constraints.cpp

@@ -80,6 +80,15 @@ BOOST_AUTO_TEST_CASE(equal_constraint_deref)
     }
 }
 
+BOOST_AUTO_TEST_CASE(equal_null_c_string)
+{
+    const char* const null_str = nullptr;
+
+    BOOST_CHECK(mock::equal(null_str).c_(null_str));
+    BOOST_CHECK(!mock::equal(null_str).c_("non-null string"));
+    BOOST_CHECK(!mock::equal("non-null-string").c_(null_str));
+}
+
 BOOST_AUTO_TEST_CASE(same_constraint)
 {
     {

test/test_log.cpp

@@ -89,6 +89,14 @@ BOOST_AUTO_TEST_CASE(strings_are_serialized_with_double_quotes)
     BOOST_CHECK_EQUAL("\"string\"", to_string(std::string("string")));
 }
 
+BOOST_AUTO_TEST_CASE(null_c_strings_are_serialized_to_nullptr)
+{
+    const char* const null_str = nullptr;
+    BOOST_CHECK_EQUAL("nullptr", to_string(null_str));
+    // Note the lack of double quotes in the output, as opposed to when the
+    // string "nullptr" is serialized.
+}
+
 namespace {
 struct non_serializable
 {};

test/test_matcher.cpp

@@ -36,7 +36,7 @@ BOOST_AUTO_TEST_CASE(ref_to_int_and_int_can_be_compared)
 namespace {
 struct fixture
 {
-    fixture() : text("same text"), actual(text.c_str())
+    fixture() : text("same text"), actual(text.c_str()), null_str(nullptr)
     {
         const char* static_string = "same text";
         BOOST_REQUIRE(actual != static_string);
@@ -44,6 +44,7 @@ struct fixture
     }
     std::string text;
     const char* actual;
+    const char* null_str;
 };
 } // namespace
 
@@ -75,6 +76,13 @@ BOOST_FIXTURE_TEST_CASE(const_char_pointer_and_std_string_can_be_compared, fixtu
     BOOST_CHECK(!match(std::string("different text"), actual));
 }
 
+BOOST_FIXTURE_TEST_CASE(null_const_char_pointers_can_be_compared, fixture)
+{
+    BOOST_CHECK(match(null_str, null_str));
+    BOOST_CHECK(!match(null_str, "non-null string"));
+    BOOST_CHECK(!match("non-null string", null_str));
+}
+
 namespace {
 template<typename T>
 std::string serialize(const T& t)