Use several unused cord instances in tests and benchmarks.

PiperOrigin-RevId: 662635356
Change-Id: I8b3d992147ee3affb92947135f09076c851448e3

absl/strings/cord_test.cc

@@ -1309,6 +1309,7 @@ TEST_P(CordTest, RemoveSuffixMakesZeroLengthNode) {
   absl::Cord c;
   c.Append(absl::Cord(std::string(100, 'x')));
   absl::Cord other_ref = c;  // Prevent inplace appends
+  EXPECT_THAT(other_ref, testing::Eq(c));
   MaybeHarden(c);
   c.Append(absl::Cord(std::string(200, 'y')));
   c.RemoveSuffix(200);
@@ -1665,6 +1666,7 @@ TEST_P(CordTest, ConstructFromExternalReleaserInvoked) {
     auto releaser = [&invoked](absl::string_view) { invoked = true; };
     {
       auto c = absl::MakeCordFromExternal("", releaser);
+      EXPECT_THAT(c, testing::Eq(""));
       EXPECT_TRUE(invoked);
     }
   }
@@ -1679,6 +1681,7 @@ TEST_P(CordTest, ConstructFromExternalReleaserInvoked) {
     auto releaser = [&invoked](absl::string_view) { invoked = true; };
     {
       auto c = absl::MakeCordFromExternal(large_dummy, releaser);
+      EXPECT_THAT(c, testing::Eq(large_dummy));
       EXPECT_FALSE(invoked);
     }
     EXPECT_TRUE(invoked);
@@ -2167,6 +2170,7 @@ TEST_P(CordTest, DiabolicalGrowth) {
   absl::Cord cord;
   for (char c : expected) {
     absl::Cord shared(cord);
+    EXPECT_THAT(cord, testing::Eq(shared));
     cord.Append(absl::string_view(&c, 1));
     MaybeHarden(cord);
   }