Googletest export

GMock: Make Truly explain when it fails

I just wrote a test that had a matcher of the form
  Optional(AllOf(
    SomeMatcher,
    SomeOtherMatcher,
    Truly(SomePredicate)))

The predicate failed, the other two matchers succeeded, and I got a hard-to-interpret message saying that the value in the optional "didn't match". Didn't match what?

This change improves situations like that slightly by having Truly explain to its result listener when it fails. When there are multiple Trulys in an AllOf, there will be some ambiguity, but it will at least provide more information than right now.

PiperOrigin-RevId: 341105141

googlemock/include/gmock/gmock-matchers.h

@@ -1453,7 +1453,7 @@ class TrulyMatcher {
   // interested in the address of the argument.
   template <typename T>
   bool MatchAndExplain(T& x,  // NOLINT
-                       MatchResultListener* /* listener */) const {
+                       MatchResultListener* listener) const {
     // Without the if-statement, MSVC sometimes warns about converting
     // a value to bool (warning 4800).
     //
@@ -1462,6 +1462,7 @@ class TrulyMatcher {
     // having no operator!().
     if (predicate_(x))
       return true;
+    *listener << "didn't satisfy the given predicate";
     return false;
   }
 

googlemock/test/gmock-matchers_test.cc

@@ -2984,6 +2984,13 @@ TEST(TrulyTest, WorksForByRefArguments) {
   EXPECT_FALSE(m.Matches(n));
 }
 
+// Tests that Truly(predicate) provides a helpful reason when it fails.
+TEST(TrulyTest, ExplainsFailures) {
+  StringMatchResultListener listener;
+  EXPECT_FALSE(ExplainMatchResult(Truly(IsPositive), -1, &listener));
+  EXPECT_EQ(listener.str(), "didn't satisfy the given predicate");
+}
+
 // Tests that Matches(m) is a predicate satisfied by whatever that
 // matches matcher m.
 TEST(MatchesTest, IsSatisfiedByWhatMatchesTheMatcher) {