diff --git a/tester/message_tester.c b/tester/message_tester.c
index 2a32d019e..bc77d9905 100644
--- a/tester/message_tester.c
+++ b/tester/message_tester.c
@@ -440,6 +440,12 @@ bool_t compare_files(const char *path1, const char *path2) {
 	return res;
 }
 
+static FILE* fopen_from_write_dir(const char * name, const char * mode) {
+	char *filepath = ms_strdup_printf("%s/%s", bc_tester_writable_dir_prefix,name);
+	FILE * file = fopen(filepath,mode);
+	ms_free(filepath);
+	return file;
+}
 static void file_transfer_message(void) {
 	LinphoneCoreManager* marie = linphone_core_manager_new( "marie_rc");
 	if (transport_supported(marie->lc, LinphoneTransportTls)) {
@@ -605,8 +611,8 @@ static void lime_file_transfer_message(void) {
 	linphone_core_enable_lime(pauline->lc, 1);
 
 	/* set the zid caches files : create two ZID cache from this valid one inserting the auto-generated sip URI for the peer account as keys in ZID cache are indexed by peer sip uri */
-	ZIDCacheMarieFD = fopen("tmpZIDCacheMarie.xml", "wb");
-	ZIDCachePaulineFD = fopen("tmpZIDCachePauline.xml", "wb");
+	ZIDCacheMarieFD = fopen_from_write_dir("tmpZIDCacheMarie.xml", "wb");
+	ZIDCachePaulineFD = fopen_from_write_dir("tmpZIDCachePauline.xml", "wb");
 	pauline_id = linphone_address_as_string_uri_only(pauline->identity);
 	marie_id = linphone_address_as_string_uri_only(marie->identity);
 	fprintf(ZIDCacheMarieFD, "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<cache><selfZID>ef7692d0792a67491ae2d44e</selfZID><peer><ZID>005dbe0399643d953a2202dd</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>%s</uri><sndKey>08df5907d30959b8cb70f6fff2d8febd88fb41b0c8afc39e4b972f86dd5cfe2d</sndKey><rcvKey>60f020a3fe11dc2cc0e1e8ed9341b4cd14944db806ca4fc95456bbe45d95c43a</rcvKey><sndSId>5f9aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>bcffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>00000078</sndIndex><rcvIndex>000001cf</rcvIndex><pvs>01</pvs></peer><peer><ZID>1234567889643d953a2202ee</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778csal_set_uuid(lc->sal, account->instance_id);bdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>%s</uri><sndKey>72d80ab1cad243cf45634980c1d02cfb2df81ce0dd5dfcf1ebeacfc5345a9176</sndKey><rcvKey>25d9ac653a83c4559cb0ae7394e7cd3b2d3c57bb28e62068d2df23e8f9b77193</rcvKey><sndSId>f69aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>22ffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>0000000f</sndIndex><rcvIndex>00000000</rcvIndex></peer></cache>", pauline_id, pauline_id);
@@ -703,10 +709,10 @@ static void lime_unit(void) {
 	/**** use functions that are not directly used by external entities ****/
 
 	/* create and load cache file */
-	CACHE = fopen("ZIDCache.xml", "wb");
+	CACHE = fopen_from_write_dir("ZIDCache.xml", "wb");
 	fprintf (CACHE, "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<cache><selfZID>ef7692d0792a67491ae2d44e</selfZID><peer><ZID>005dbe0399643d953a2202dd</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>pipo1@pipo.com</uri><sndKey>963c57bb28e62068d2df23e8f9b771932d3c57bb28e62068d2df23e8f9b77193</sndKey><rcvKey>05d9ac653a83c4559cb0ae7394e7cd3b2d3c57bb28e62068d2df23e8f9b77193</rcvKey><sndSId>5f9aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>02ffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>00000069</sndIndex><rcvIndex>000001e8</rcvIndex><pvs>01</pvs></peer><peer><ZID>1234567889643d953a2202ee</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>pipo1@pipo.com</uri><sndKey>123456789012345678901234567890123456765431262068d2df23e8f9b77193</sndKey><rcvKey>25d9ac653a83c4559cb0ae7394e7cd3b2d3c57bb28e62068d2df23e8f9b77193</rcvKey><sndSId>f69aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>22ffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>00000001</sndIndex><rcvIndex>00000000</rcvIndex><pvs>01</pvs></peer></cache>");
 	fclose(CACHE);
-	CACHE = fopen("ZIDCache.xml", "rb+");
+	CACHE = fopen_from_write_dir("ZIDCache.xml", "rb+");
 	cacheBufferString = (uint8_t*) ms_load_file_content(CACHE, &size);
 	*(cacheBufferString+size) = '\0';
 	fclose(CACHE);
@@ -771,7 +777,7 @@ static void lime_unit(void) {
 	/* dump the xml document into a string */
 	xmlDocDumpFormatMemoryEnc(cacheBuffer, &xmlStringOutput, &xmlStringLength, "UTF-8", 0);
 	/* write it to the file */
-	CACHE = fopen("ZIDCache.xml", "w+");
+	CACHE = fopen_from_write_dir("ZIDCache.xml", "w+");
 	fwrite(xmlStringOutput, 1, xmlStringLength, CACHE);
 	xmlFree(xmlStringOutput);
 	fclose(CACHE);
@@ -779,10 +785,10 @@ static void lime_unit(void) {
 
 	/**** Higher level tests using 2 caches to encrypt/decrypt a message ****/
 	/* Create Alice cache file and then load it */
-	CACHE = fopen("ZIDCacheAlice.xml", "wb");
+	CACHE = fopen_from_write_dir("ZIDCacheAlice.xml", "wb");
 	fprintf(CACHE, "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<cache><selfZID>ef7692d0792a67491ae2d44e</selfZID><peer><ZID>005dbe0399643d953a2202dd</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>sip:pauline@sip.example.org</uri><sndKey>9111ebeb52e50edcc6fcb3eea1a2d3ae3c2c75d3668923e83c59d0f472455150</sndKey><rcvKey>60f020a3fe11dc2cc0e1e8ed9341b4cd14944db806ca4fc95456bbe45d95c43a</rcvKey><sndSId>5f9aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>bcffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>00000080</sndIndex><rcvIndex>000001cf</rcvIndex><pvs>01</pvs></peer><peer><ZID>1234567889643d953a2202ee</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>sip:pauline@sip.example.org</uri><sndKey>72d80ab1cad243cf45634980c1d02cfb2df81ce0dd5dfcf1ebeacfc5345a9176</sndKey><rcvKey>25d9ac653a83c4559cb0ae7394e7cd3b2d3c57bb28e62068d2df23e8f9b77193</rcvKey><sndSId>f69aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>22ffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>0000000f</sndIndex><rcvIndex>00000000</rcvIndex></peer></cache>");
 	fclose(CACHE);
-	CACHE = fopen("ZIDCacheAlice.xml", "rb+");
+	CACHE = fopen_from_write_dir("ZIDCacheAlice.xml", "rb+");
 	cacheBufferString = (uint8_t *)ms_load_file_content(CACHE, &size);
 	*(cacheBufferString+size) = '\0';
 	fclose(CACHE);
@@ -791,10 +797,10 @@ static void lime_unit(void) {
 	ms_free(cacheBufferString);
 
 	/* Create Bob cache file and then load it */
-	CACHE = fopen("ZIDCacheBob.xml", "wb");
+	CACHE = fopen_from_write_dir("ZIDCacheBob.xml", "wb");
 	fprintf(CACHE, "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<cache><selfZID>005dbe0399643d953a2202dd</selfZID><peer><ZID>ef7692d0792a67491ae2d44e</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>sip:marie@sip.example.org</uri><rcvKey>9111ebeb52e50edcc6fcb3eea1a2d3ae3c2c75d3668923e83c59d0f472455150</rcvKey><sndKey>60f020a3fe11dc2cc0e1e8ed9341b4cd14944db806ca4fc95456bbe45d95c43a</sndKey><rcvSId>5f9aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndSId>bcffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvIndex>00000080</rcvIndex><sndIndex>000001cf</sndIndex><pvs>01</pvs></peer><peer><ZID>1234567889643d953a2202ee</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>sip:marie@sip.example.org</uri><sndKey>81e6e6362c34dc974263d1f77cbb9a8d6d6a718330994379099a8fa19fb12faa</sndKey><rcvKey>25d9ac653a83c4559cb0ae7394e7cd3b2d3c57bb28e62068d2df23e8f9b77193</rcvKey><sndSId>f69aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>22ffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>0000002e</sndIndex><rcvIndex>00000000</rcvIndex><pvs>01</pvs></peer></cache>");
 	fclose(CACHE);
-	CACHE = fopen("ZIDCacheBob.xml", "rb+");
+	CACHE = fopen_from_write_dir("ZIDCacheBob.xml", "rb+");
 	cacheBufferString = (uint8_t *)ms_load_file_content(CACHE, &size);
 	*(cacheBufferString+size) = '\0';
 	fclose(CACHE);
@@ -827,7 +833,7 @@ static void lime_unit(void) {
 	/* dump the xml document into a string */
 	xmlDocDumpFormatMemoryEnc(cacheBufferAlice, &xmlStringOutput, &xmlStringLength, "UTF-8", 0);
 	/* write it to the file */
-	CACHE = fopen("ZIDCacheAlice.xml", "wb+");
+	CACHE = fopen_from_write_dir("ZIDCacheAlice.xml", "wb+");
 	fwrite(xmlStringOutput, 1, xmlStringLength, CACHE);
 	xmlFree(xmlStringOutput);
 	fclose(CACHE);
@@ -856,8 +862,8 @@ static void lime_text_message(void) {
 	linphone_core_enable_lime(pauline->lc, 1);
 
 	/* set the zid caches files : create two ZID cache from this valid one inserting the auto-generated sip URI for the peer account as keys in ZID cache are indexed by peer sip uri */
-	ZIDCacheMarieFD = fopen("tmpZIDCacheMarie.xml", "w");
-	ZIDCachePaulineFD = fopen("tmpZIDCachePauline.xml", "w");
+	ZIDCacheMarieFD = fopen_from_write_dir("tmpZIDCacheMarie.xml", "w");
+	ZIDCachePaulineFD = fopen_from_write_dir("tmpZIDCachePauline.xml", "w");
 	fprintf(ZIDCacheMarieFD, "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<cache><selfZID>ef7692d0792a67491ae2d44e</selfZID><peer><ZID>005dbe0399643d953a2202dd</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>%s</uri><sndKey>08df5907d30959b8cb70f6fff2d8febd88fb41b0c8afc39e4b972f86dd5cfe2d</sndKey><rcvKey>60f020a3fe11dc2cc0e1e8ed9341b4cd14944db806ca4fc95456bbe45d95c43a</rcvKey><sndSId>5f9aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>bcffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>00000078</sndIndex><rcvIndex>000001cf</rcvIndex><pvs>01</pvs></peer><peer><ZID>1234567889643d953a2202ee</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>%s</uri><sndKey>72d80ab1cad243cf45634980c1d02cfb2df81ce0dd5dfcf1ebeacfc5345a9176</sndKey><rcvKey>25d9ac653a83c4559cb0ae7394e7cd3b2d3c57bb28e62068d2df23e8f9b77193</rcvKey><sndSId>f69aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>22ffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>0000000f</sndIndex><rcvIndex>00000000</rcvIndex></peer></cache>", linphone_address_as_string_uri_only(pauline->identity), linphone_address_as_string_uri_only(pauline->identity));
 	fprintf(ZIDCachePaulineFD, "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<cache><selfZID>005dbe0399643d953a2202dd</selfZID><peer><ZID>ef7692d0792a67491ae2d44e</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>%s</uri><rcvKey>08df5907d30959b8cb70f6fff2d8febd88fb41b0c8afc39e4b972f86dd5cfe2d</rcvKey><sndKey>60f020a3fe11dc2cc0e1e8ed9341b4cd14944db806ca4fc95456bbe45d95c43a</sndKey><rcvSId>5f9aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndSId>bcffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvIndex>00000078</rcvIndex><sndIndex>000001cf</sndIndex><pvs>01</pvs></peer><peer><ZID>1234567889643d953a2202ee</ZID><rs1>9b5c8f06f3b6c2c695f2dfc3c26f31f5fef8661f8c5fe7c95aeb5c5b0435b045</rs1><aux>f8324dd18ea905171ec2be89f879d01d5994132048d92ea020778cbdf31c605e</aux><rs2>2fdcef69380937c2cf221f7d11526f286c39f49641452ba9012521c705094899</rs2><uri>%s</uri><sndKey>81e6e6362c34dc974263d1f77cbb9a8d6d6a718330994379099a8fa19fb12faa</sndKey><rcvKey>25d9ac653a83c4559cb0ae7394e7cd3b2d3c57bb28e62068d2df23e8f9b77193</rcvKey><sndSId>f69aa1e5e4c7ec88fa389a9f6b8879b42d3c57bb28e62068d2df23e8f9b77193</sndSId><rcvSId>22ffd51e7316a6c6f53a50fcf01b01bf2d3c57bb28e62068d2df23e8f9b77193</rcvSId><sndIndex>0000002e</sndIndex><rcvIndex>00000000</rcvIndex><pvs>01</pvs></peer></cache>", linphone_address_as_string_uri_only(marie->identity), linphone_address_as_string_uri_only(marie->identity));
 	fclose(ZIDCacheMarieFD);