GH-50440: [C++][Gandiva] cover timestamp and time cast error paths

Signed-off-by: abdul rawoof <abdulr@bugqore.com>

Author: Arawoof06

cpp/src/gandiva/precompiled/time_test.cc

@@ -81,6 +81,38 @@ TEST(TestTime, TestCastDateInvalidUnterminated) {
   context.Reset();
 }
 
+TEST(TestTime, TestCastTimestampInvalidUnterminated) {
+  ExecutionContext context;
+  int64_t context_ptr = reinterpret_cast<int64_t>(&context);
+
+  // castTIMESTAMP_utf8 reaches the same set_error_for_date helper, so exercise
+  // the over-read path from that entry point with an unterminated buffer too.
+  const std::string value = "2000-01-01 24:00:00";
+  const auto length = static_cast<int32_t>(value.size());
+  std::unique_ptr<char[]> input(new char[length]);
+  std::memcpy(input.get(), value.data(), length);
+
+  EXPECT_EQ(castTIMESTAMP_utf8(context_ptr, input.get(), length), 0);
+  EXPECT_EQ(context.get_error(),
+            "Not a valid time for timestamp value 2000-01-01 24:00:00");
+  context.Reset();
+}
+
+TEST(TestTime, TestCastTimeInvalidUnterminated) {
+  ExecutionContext context;
+  int64_t context_ptr = reinterpret_cast<int64_t>(&context);
+
+  // castTIME_utf8 reaches set_error_for_date as well.
+  const std::string value = "24H00H00";
+  const auto length = static_cast<int32_t>(value.size());
+  std::unique_ptr<char[]> input(new char[length]);
+  std::memcpy(input.get(), value.data(), length);
+
+  EXPECT_EQ(castTIME_utf8(context_ptr, input.get(), length), 0);
+  EXPECT_EQ(context.get_error(), "Invalid character in time 24H00H00");
+  context.Reset();
+}
+
 TEST(TestTime, TestCastTimestamp) {
   ExecutionContext context;
   int64_t context_ptr = reinterpret_cast<int64_t>(&context);