diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index d164e9f8f..cd7731e6b 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -114,16 +114,6 @@ extern "C" {
#define MBEDTLS_ERR_ERROR_GENERIC_ERROR -0x0001 /**< Generic error */
#define MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED -0x006E /**< This is a bug in the library */
-#if defined(MBEDTLS_TEST_HOOKS)
-void (*mbedtls_test_err_add_hook)( int, int, const char *, int );
-int mbedtls_err_add( int high, int low, const char *file, int line );
-#define MBEDTLS_ERR_ADD( high, low ) \
- ( mbedtls_err_add( high, low, __FILE__, __LINE__ ) )
-#else
-#define MBEDTLS_ERR_ADD( high, low ) \
- ( high + low )
-#endif
-
/**
* \brief Translate a mbed TLS error code into a string representation,
* Result is truncated if necessary and always includes a terminating
diff --git a/library/common.c b/library/common.c
new file mode 100644
index 000000000..9f901f006
--- /dev/null
+++ b/library/common.c
@@ -0,0 +1,27 @@
+/*
+ * Internal invasive testing helper functions
+ *
+ * Copyright The Mbed TLS Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if defined(MBEDTLS_TEST_HOOKS)
+void (*mbedtls_test_err_add_hook)( int, int, const char *, int );
+int mbedtls_err_add( int high, int low, const char *file, int line ) {
+ if( mbedtls_test_err_add_hook != NULL )
+ (*mbedtls_test_err_add_hook)( high, low, file, line );
+ return ( high + low );
+}
+#endif
diff --git a/library/common.h b/library/common.h
index 5845766ac..f4cef97b9 100644
--- a/library/common.h
+++ b/library/common.h
@@ -29,6 +29,7 @@
#include "mbedtls/config.h"
#endif
+#if defined(MBEDTLS_TEST_HOOKS)
/** Helper to define a function as static except when building invasive tests.
*
* If a function is only used inside its own source file and should be
@@ -44,10 +45,25 @@
* #endif
* ```
*/
-#if defined(MBEDTLS_TEST_HOOKS)
#define MBEDTLS_STATIC_TESTABLE
+
+/** Helper macro and function to combine a high and low level error code.
+ *
+ * This function uses a hook (`mbedtls_test_err_add_hook`) to allow invasive
+ * testing of its inputs. This is used in the test infrastructure to report
+ * on errors when combining two error codes of the same level (e.g: two high
+ * or two low level errors).
+ */
+int mbedtls_err_add( int high, int low, const char *file, int line );
+#define MBEDTLS_ERR_ADD( high, low ) \
+ ( mbedtls_err_add( high, low, __FILE__, __LINE__ ) )
+
#else
#define MBEDTLS_STATIC_TESTABLE static
-#endif
+
+#define MBEDTLS_ERR_ADD( high, low ) \
+ ( high + low )
+
+#endif /* MBEDTLS_TEST_HOOKS */
#endif /* MBEDTLS_LIBRARY_COMMON_H */
diff --git a/library/error.c b/library/error.c
index 486afedfa..901a3699a 100644
--- a/library/error.c
+++ b/library/error.c
@@ -210,13 +210,6 @@
#include "mbedtls/xtea.h"
#endif
-#if defined(MBEDTLS_TEST_HOOKS)
-int mbedtls_err_add( int high, int low, const char *file, int line ) {
- if( mbedtls_test_err_add_hook != NULL )
- (*mbedtls_test_err_add_hook)( high, low, file, line );
- return ( high + low );
-}
-#endif
const char * mbedtls_high_level_strerr( int error_code )
{
diff --git a/tests/include/test/helpers.h b/tests/include/test/helpers.h
index 1fe25d89f..a26f1eeda 100644
--- a/tests/include/test/helpers.h
+++ b/tests/include/test/helpers.h
@@ -280,9 +280,9 @@ void mbedtls_test_mutex_usage_check( void );
#if defined(MBEDTLS_TEST_HOOKS)
/**
- * \brief Check that a pure high-level error code is being combined with a
- * pure low-level error code as otherwise the resultant error code
- * would be corrupted.
+ * \brief Check that a pure high-level error code is being combined with a
+ * pure low-level error code as otherwise the resultant error code
+ * would be corrupted.
*/
void mbedtls_test_err_add_check( int high, int low,
const char *file, int line);
diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index 6a4758af9..b35b1437f 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -33,10 +33,6 @@
#include "psa/crypto.h"
#endif /* MBEDTLS_USE_PSA_CRYPTO */
-#if defined(MBEDTLS_TEST_HOOKS)
-#include "mbedtls/error.h"
-#endif
-
/* Test code may use deprecated identifiers only if the preprocessor symbol
* MBEDTLS_TEST_DEPRECATED is defined. When building tests, set
* MBEDTLS_TEST_DEPRECATED explicitly if MBEDTLS_DEPRECATED_WARNING is
diff --git a/visualc/VS2010/mbedTLS.vcxproj b/visualc/VS2010/mbedTLS.vcxproj
index cb819a8bd..9cf432915 100644
--- a/visualc/VS2010/mbedTLS.vcxproj
+++ b/visualc/VS2010/mbedTLS.vcxproj
@@ -293,6 +293,7 @@
+