Associate unit test data dir with a more specific variable

Having 'TESTS', the Automake variable and 'TESTS' the unit test data dir
seems confusing, lets rename the latter to to 'TESTS_DIR'.

Makefile.tests

@@ -3,7 +3,7 @@
 
 AM_CPPFLAGS +=					\
 	$(CMOCKA_CFLAGS)			\
-	-DTESTS=\"$(abs_srcdir)\"		\
+	-DTESTS_DIR=\"$(abs_srcdir)\"		\
 	-DNAMED_PLUGINDIR=\"$(libdir)/named\"
 
 LDADD =			\

lib/dns/tests/dnstest.c

@@ -179,7 +179,7 @@ dns_test_begin(FILE *logfile, bool start_managers) {
 	 * that access test data files must first chdir to the proper
 	 * location.
 	 */
-	if (chdir(TESTS) == -1) {
+	if (chdir(TESTS_DIR) == -1) {
 		CHECK(ISC_R_FAILURE);
 	}
 

lib/irs/tests/resconf_test.c

@@ -39,7 +39,7 @@ setup_test(void) {
 	 * that access test data files must first chdir to the proper
 	 * location.
 	 */
-	assert_return_code(chdir(TESTS), 0);
+	assert_return_code(chdir(TESTS_DIR), 0);
 }
 
 /* test irs_resconf_load() */

lib/isc/tests/file_test.c

@@ -57,7 +57,7 @@ isc_file_sanitize_test(void **state) {
 
 	UNUSED(state);
 
-	assert_return_code(chdir(TESTS), 0);
+	assert_return_code(chdir(TESTS_DIR), 0);
 
 	result = isc_file_sanitize("testdata/file", NAME, "test", buf, 1024);
 	assert_int_equal(result, ISC_R_SUCCESS);
@@ -93,7 +93,7 @@ isc_file_template_test(void **state) {
 
 	UNUSED(state);
 
-	assert_return_code(chdir(TESTS), 0);
+	assert_return_code(chdir(TESTS_DIR), 0);
 
 	result = isc_file_template("/absolute/path", "file-XXXXXXXX", buf,
 				   sizeof(buf));

lib/ns/tests/nstest.c

@@ -315,7 +315,7 @@ ns_test_begin(FILE *logfile, bool start_managers) {
 	 * that access test data files must first chdir to the proper
 	 * location.
 	 */
-	if (chdir(TESTS) == -1) {
+	if (chdir(TESTS_DIR) == -1) {
 		CHECK(ISC_R_FAILURE);
 	}