Rename the 'no entropy' feature to MBEDTLS_TEST_NULL_ENTROPY

Following review and for clarity, changed the name of the feature to 'null
entropy'.

include/mbedtls/check_config.h

@@ -130,15 +130,14 @@
 #error "MBEDTLS_ENTROPY_FORCE_SHA256 defined, but not all prerequisites"
 #endif
 
-#if defined(MBEDTLS_TEST_WO_ENTROPY)
-#warning "MBEDTLS_TEST_WO_ENTROPY defined, this build provides no security!"
-#if !defined(MBEDTLS_ENTROPY_C) || !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
-#error "MBEDTLS_TEST_WO_ENTROPY defined, but not all prerequisites"
-#endif
-#if defined(MBEDTLS_ENTROPY_NV_SEED) || defined(MBEDTLS_ENTROPY_HARDWARE_ALT) || \
-    defined(MBEDTLS_HAVEGE_C)
-#error "MBEDTLS_TEST_WO_ENTROPY defined, but entropy sources too"
+#if defined(MBEDTLS_TEST_NULL_ENTROPY) && \
+    ( !defined(MBEDTLS_ENTROPY_C) || !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES) )
+#error "MBEDTLS_TEST_NULL_ENTROPY defined, but not all prerequisites"
 #endif
+#if defined(MBEDTLS_TEST_NULL_ENTROPY) && \
+     ( defined(MBEDTLS_ENTROPY_NV_SEED) || defined(MBEDTLS_ENTROPY_HARDWARE_ALT) || \
+    defined(MBEDTLS_HAVEGE_C) )
+#error "MBEDTLS_TEST_NULL_ENTROPY defined, but entropy sources too"
 #endif
 
 #if defined(MBEDTLS_GCM_C) && (                                        \

include/mbedtls/config.h

@@ -280,29 +280,21 @@
 //#define MBEDTLS_AES_DECRYPT_ALT
 
 /**
- * \def MBEDTLS_TEST_WO_ENTROPY
+ * \def MBEDTLS_TEST_NULL_ENTROPY
  *
- * Enable testing mbed TLS without access to any entropy. This enables testing
- * the library before the platforms entropy sources are integrated (, see for
- * example the MBEDTLS_ENTROPY_HARDWARE_ALT or the MBEDTLS_ENTROPY_NV_SEED
- * switch).
+ * Enables testing and use of mbed TLS without any configured entropy sources.
+ * This permits use of the library on platforms before an entropy source has
+ * been integrated (see for example the MBEDTLS_ENTROPY_HARDWARE_ALT or the
+ * MBEDTLS_ENTROPY_NV_SEED switches).
+ *
+ * WARNING! This switch MUST be disabled in production builds, and is suitable
+ * only for development.
+ * Enabling the switch negates any security provided by the library.
  *
  * Requires MBEDTLS_ENTROPY_C, MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
  *
- * WARNING! This switch is extremely DANGEROUS, don't use it in production code
- * under any circumstances. This switch nullifies any security provided by the
- * library.
  */
-//#define MBEDTLS_TEST_WO_ENTROPY
-
-
-/**
- * \def MBEDTLS_ENTROPY_NV_SEED
- *
- * Strong software entropy source. It is not yet implemented,
- * adding it because it is mutually exclusive with MBEDTLS_TEST_WO_ENTROPY.
- */
-//#define MBEDTLS_ENTROPY_NV_SEED
+//#define MBEDTLS_TEST_NULL_ENTROPY
 
 /**
  * \def MBEDTLS_ENTROPY_HARDWARE_ALT

include/mbedtls/entropy_poll.h

@@ -46,7 +46,7 @@ extern "C" {
 /**
  * \brief           Entropy poll callback that provides 0 entropy.
  */
-#if defined(MBEDTLS_TEST_WO_ENTROPY)
+#if defined(MBEDTLS_TEST_NULL_ENTROPY)
     int mbedtls_zero_entropy_poll( void *data,
                                 unsigned char *output, size_t len, size_t *olen );
 #endif