diff --git a/libc/test/src/string/memcmp_test.cpp b/libc/test/src/string/memcmp_test.cpp
--- a/libc/test/src/string/memcmp_test.cpp
+++ b/libc/test/src/string/memcmp_test.cpp
@@ -9,7 +9,6 @@
 #include "memory_utils/memory_check_utils.h"
 #include "src/string/memcmp.h"
 #include "test/UnitTest/Test.h"
-#include "test/UnitTest/TestLogger.h"
 
 namespace __llvm_libc {
 
@@ -52,10 +51,7 @@
   for (size_t size = 0; size < kMaxSize; ++size) {
     auto span1 = Buffer1.span().subspan(0, size);
     auto span2 = Buffer2.span().subspan(0, size);
-    const bool OK = CheckMemcmp<Impl>(span1, span2, size);
-    if (!OK)
-      testing::tlog << "Failed at size=" << size << '\n';
-    ASSERT_TRUE(OK);
+    ASSERT_TRUE(CheckMemcmp<Impl>(span1, span2, size));
   }
 }
 
diff --git a/libc/test/src/string/memory_utils/memory_check_utils.h b/libc/test/src/string/memory_utils/memory_check_utils.h
--- a/libc/test/src/string/memory_utils/memory_check_utils.h
+++ b/libc/test/src/string/memory_utils/memory_check_utils.h
@@ -12,6 +12,7 @@
 #include "src/__support/CPP/span.h"
 #include "src/__support/macros/sanitizer.h"
 #include "src/string/memory_utils/utils.h"
+#include "test/UnitTest/TestLogger.h"
 #include <stddef.h> // size_t
 #include <stdint.h> // uintxx_t
 #include <stdlib.h> // malloc/free
@@ -82,8 +83,11 @@
   Randomize(dst);
   FnImpl(dst, src, size);
   for (size_t i = 0; i < size; ++i)
-    if (dst[i] != src[i])
+    if (dst[i] != src[i]) {
+      testing::tlog << "memcpy error\n"
+                    << "size=" << size << ", mismatch_index=" << i << '\n';
       return false;
+    }
   return true;
 }
 
@@ -92,26 +96,36 @@
 bool CheckMemset(cpp::span<char> dst, uint8_t value, size_t size) {
   Randomize(dst);
   FnImpl(dst, value, size);
-  for (char c : dst)
-    if (c != (char)value)
+  for (size_t i = 0; i < size; ++i)
+    if (dst[i] != (char)value) {
+      testing::tlog << "memset error\n"
+                    << "size=" << size << ", mismatch_index=" << i << '\n';
       return false;
+    }
   return true;
 }
 
 // Checks that FnImpl implements the bcmp semantic.
 template <auto FnImpl>
 bool CheckBcmp(cpp::span<char> span1, cpp::span<char> span2, size_t size) {
+  const auto error = [=](const char *msg, int cmp,
+                         size_t mismatch_index) -> bool {
+    testing::tlog << "bcmp error : " << msg << '\n'
+                  << "cmp=" << cmp << ", size=" << size
+                  << ", mismatch_index=" << mismatch_index << '\n';
+    return false;
+  };
   ReferenceCopy(span2, span1);
   // Compare equal
   if (int cmp = FnImpl(span1, span2, size); cmp != 0)
-    return false;
+    return error("buffer are equal expected cmp == 0", cmp, 0);
   // Compare not equal if any byte differs
   for (size_t i = 0; i < size; ++i) {
     ++span2[i];
     if (int cmp = FnImpl(span1, span2, size); cmp == 0)
-      return false;
+      return error("buffer are equal expected cmp != 0", cmp, i);
     if (int cmp = FnImpl(span2, span1, size); cmp == 0)
-      return false;
+      return error("buffer are equal expected cmp != 0", cmp, i);
     --span2[i];
   }
   return true;
@@ -120,24 +134,31 @@
 // Checks that FnImpl implements the memcmp semantic.
 template <auto FnImpl>
 bool CheckMemcmp(cpp::span<char> span1, cpp::span<char> span2, size_t size) {
+  const auto error = [=](const char *msg, int cmp,
+                         size_t mismatch_index) -> bool {
+    testing::tlog << "memcmp error : " << msg << '\n'
+                  << "cmp=" << cmp << ", size=" << size
+                  << ", mismatch_index=" << mismatch_index << '\n';
+    return false;
+  };
   ReferenceCopy(span2, span1);
   // Compare equal
   if (int cmp = FnImpl(span1, span2, size); cmp != 0)
-    return false;
+    return error("buffer are equal expected cmp == 0", cmp, 0);
   // Compare not equal if any byte differs
   for (size_t i = 0; i < size; ++i) {
     ++span2[i];
     int ground_truth = __builtin_memcmp(span1.data(), span2.data(), size);
     if (ground_truth > 0) {
       if (int cmp = FnImpl(span1, span2, size); cmp <= 0)
-        return false;
+        return error("buffer are different, expected cmp > 0", cmp, i);
       if (int cmp = FnImpl(span2, span1, size); cmp >= 0)
-        return false;
+        return error("buffer are different, expected cmp < 0", cmp, i);
     } else {
       if (int cmp = FnImpl(span1, span2, size); cmp >= 0)
-        return false;
+        return error("buffer are different, expected cmp < 0", cmp, i);
       if (int cmp = FnImpl(span2, span1, size); cmp <= 0)
-        return false;
+        return error("buffer are different, expected cmp > 0", cmp, i);
     }
     --span2[i];
   }