--- a/tests.c	Mon Feb 22 18:43:46 2016 +0200
+++ b/tests.c	Mon Feb 22 19:39:14 2016 +0200
@@ -9,10 +9,13 @@
 #define SET_SENTINEL_BYTE 0x0e5
 
 
+typedef struct
+{
+    char *header, *res;
+} test_ctx;
+
+
 // Globals
-char *test_str_header = NULL,
-     *test_str_res = NULL;
-
 int tests_failed, tests_passed, tests_total, tests_sets, tests_nenabled;
 int tests_enabled[SET_MAX_TESTS];
 
@@ -93,61 +96,67 @@
 }
 
 
-void test_start_v(const char *fmt, va_list ap)
+void test_init(test_ctx *ctx)
+{
+    memset(ctx, 0, sizeof(test_ctx));
+}
+
+
+void test_start_v(test_ctx *ctx, const char *fmt, va_list ap)
 {
     tests_total++;
 
-    th_free_r(&test_str_header);
-    th_free_r(&test_str_res);
+    th_free_r(&ctx->header);
+    th_free_r(&ctx->res);
 
-    test_str_header = th_strdup_vprintf(fmt, ap);
+    ctx->header = th_strdup_vprintf(fmt, ap);
 }
 
 
-void test_start(const char *fmt, ...)
+void test_start(test_ctx *ctx, const char *fmt, ...)
 {
     va_list ap;
     va_start(ap, fmt);
-    test_start_v(fmt, ap);
+    test_start_v(ctx, fmt, ap);
     va_end(ap);
 }
 
 
-void test_result_msg_v(BOOL check, const char *fmt, va_list ap)
+void test_result_msg_v(test_ctx *ctx, BOOL check, const char *fmt, va_list ap)
 {
     if (check)
     {
-        THPRINT(2, "%s: OK\n", test_str_header);
+        THPRINT(2, "%s: OK\n", ctx->header);
         tests_passed++;
     }
     else
     {
-        THPRINT(0, "%s: FAIL\n", test_str_header);
+        THPRINT(0, "%s: FAIL\n", ctx->header);
         if (fmt != NULL)
         {
             THPRINT(0, "  - ");
             THPRINT_V(0, fmt, ap);
             THPRINT(0, "\n");
         }
-        if (test_str_res != NULL)
-            THPRINT(0, "%s\n", test_str_res);
+        if (ctx->res != NULL)
+            THPRINT(0, "%s\n", ctx->res);
         tests_failed++;
     }
 }
 
 
-void test_result_msg(BOOL check, const char *fmt, ...)
+void test_result_msg(test_ctx *ctx, BOOL check, const char *fmt, ...)
 {
     va_list ap;
     va_start(ap, fmt);
-    test_result_msg_v(check, fmt, ap);
+    test_result_msg_v(ctx, check, fmt, ap);
     va_end(ap);
 }
 
 
-void test_result(BOOL check)
+void test_result(test_ctx *ctx, BOOL check)
 {
-    test_result_msg_v(check, NULL, NULL);
+    test_result_msg_v(ctx, check, NULL, NULL);
 }
 
 
@@ -156,9 +165,11 @@
 {
     int ret1, ret2;
     va_list tmp;
+    test_ctx ctx;
 
     // Test basic *printf() functionality
-    test_start("th_vsnprintf('%s', %s)", fmt, msg);
+    test_init(&ctx);
+    test_start(&ctx, "th_vsnprintf('%s', %s)", fmt, msg);
 
     memset(buf1, SET_SENTINEL_BYTE, SET_BUF_SIZE+2); buf1[SET_BUF_SIZE+1] = 0;
     memset(buf2, SET_SENTINEL_BYTE, SET_BUF_SIZE+2); buf2[SET_BUF_SIZE+1] = 0;
@@ -168,16 +179,16 @@
     ret1 = th_vsnprintf(buf1, len, fmt, ap);
     ret2 = vsnprintf(buf2, len, fmt, tmp);
 
-    test_result_msg(ret1 == ret2, "retval mismatch %d != %d", ret1, ret2);
-    test_result_msg(strcmp(buf1, buf2) == 0, "result mismatch '%s' != '%s'", buf1, buf2);
+    test_result_msg(&ctx, ret1 == ret2, "retval mismatch %d [th] != %d [libc]", ret1, ret2);
+    test_result_msg(&ctx, strcmp(buf1, buf2) == 0, "result mismatch '%s' [th] != '%s' [libc]", buf1, buf2);
 
-    test_result_msg((unsigned char) buf1[len] == SET_SENTINEL_BYTE, "buffer #1 overflow, sentinel 0x%02x", buf1[len]);
-    test_result_msg((unsigned char) buf2[len] == SET_SENTINEL_BYTE, "buffer #2 overflow, sentinel 0x%02x", buf2[len]);
+    test_result_msg(&ctx, (unsigned char) buf1[len] == SET_SENTINEL_BYTE, "buffer #1 overflow, sentinel 0x%02x", buf1[len]);
+    test_result_msg(&ctx, (unsigned char) buf2[len] == SET_SENTINEL_BYTE, "buffer #2 overflow, sentinel 0x%02x", buf2[len]);
 
     // Test th_strdup_vprintf()
-    test_start("th_strdup_vprintf('%s')", fmt);
+    test_start(&ctx, "th_strdup_vprintf('%s')", fmt);
     char *str = th_strdup_vprintf(fmt, ap);
-    test_result_msg(str != NULL, "result NULL");
+    test_result_msg(&ctx, str != NULL, "result NULL");
     th_free(str);
 }
 
@@ -216,18 +227,21 @@
 
 
 #define TEST2(fun, str1, str2, ret) do { \
-        test_start(# fun  "('%s', '%s')", str1, str2); \
-        test_result(( fun (str1, str2) == 0) == ret); \
+        test_ctx ctx; test_init(&ctx); \
+        test_start(&ctx, # fun  "('%s', '%s')", str1, str2); \
+        test_result(&ctx, ( fun (str1, str2) == 0) == ret); \
     } while (0)
 
 #define TEST2B(fun, str1, str2, ret) do { \
-        test_start(# fun  "('%s', '%s')", str1, str2); \
-        test_result( fun (str1, str2) == ret); \
+        test_ctx ctx; test_init(&ctx); \
+        test_start(&ctx, # fun  "('%s', '%s')", str1, str2); \
+        test_result(&ctx, fun (str1, str2) == ret); \
     } while (0)
 
 #define TEST3(fun, str1, str2, len, ret) do { \
-        test_start(# fun  "('%s', '%s', %d)", str1, str2, len); \
-        test_result(( fun (str1, str2, len) == 0) == ret); \
+        test_ctx ctx; test_init(&ctx); \
+        test_start(&ctx, # fun  "('%s', '%s', %d)", str1, str2, len); \
+        test_result(&ctx, ( fun (str1, str2, len) == 0) == ret); \
     } while (0)