remove mrb_open NULL check for small test programs. They are only for proof-on-concept test, not production code. Adding precise checks are not needed for those code

src/codegen.c

@@ -2292,11 +2292,6 @@ main()
   mrb_state *mrb = mrb_open();
   int n;
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting codegen test");
-    return EXIT_FAILURE;
-  }
-
 #if 1
   n = mrb_compile_string(mrb, "p(__FILE__)\np(__LINE__)");
 #else

src/gc.c

@@ -934,11 +934,6 @@ test_mrb_field_write_barrier(void)
   mrb_state *mrb = mrb_open();
   struct RBasic *obj, *value;
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting test_mrb_field_write_barrier");
-    return;
-  }
-
   puts("test_mrb_field_write_barrier");
   obj = RBASIC(mrb_ary_new(mrb));
   value = RBASIC(mrb_str_new_cstr(mrb, "value"));
@@ -1002,11 +997,6 @@ test_mrb_write_barrier(void)
   mrb_state *mrb = mrb_open();
   struct RBasic *obj;
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting test_mrb_write_barrier");
-    return;
-  }
-
   puts("test_mrb_write_barrier");
   obj = RBASIC(mrb_ary_new(mrb));
   paint_black(obj);
@@ -1034,11 +1024,6 @@ test_add_gray_list(void)
   mrb_state *mrb = mrb_open();
   struct RBasic *obj1, *obj2;
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting test_add_gray_list");
-    return;
-  }
-
   puts("test_add_gray_list");
   gc_assert(mrb->gray_list == NULL);
   obj1 = RBASIC(mrb_str_new_cstr(mrb, "test"));
@@ -1063,11 +1048,6 @@ test_gc_gray_mark(void)
   struct RBasic *obj;
   size_t gray_num = 0;
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting test_gc_gray_mark");
-    return;
-  }
-
   puts("test_gc_gray_mark");
 
   puts("  in MRB_TT_CLASS");
@@ -1099,11 +1079,6 @@ test_incremental_gc(void)
   RVALUE *free;
   struct heap_page *page;
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting test_incremental_gc");
-    return;
-  }
-
   puts("test_incremental_gc");
 
   mrb_garbage_collect(mrb);
@@ -1160,11 +1135,6 @@ test_incremental_sweep_phase(void)
 {
   mrb_state *mrb = mrb_open();
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting test_incremental_sweep_phase");
-    return;
-  }
-
   puts("test_incremental_sweep_phase");
 
   add_heap(mrb);
@@ -1188,11 +1158,6 @@ test_gc_api(void)
 
   mrb_value argv[1];
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting test_gc_api");
-    return;
-  }
-
   puts("test_gc_api");
 
   gc_start(mrb, mrb_nil_value());
@@ -1226,11 +1191,6 @@ test_many_object_benchmark(void)
   mrb_value ary = mrb_ary_new(mrb);
   int save_point = mrb_gc_arena_save(mrb);
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, test_many_object_benchmark");
-    return;
-  }
-
   puts("test_many_object_benchmark");
 
   for (i=0; i<1000; i++) {

src/parse.y

@@ -5518,11 +5518,6 @@ main()
   mrb_state *mrb = mrb_open();
   int n;
 
-  if (mrb == NULL) {
-    fprintf(stderr, "Invalid mrb_state, exiting parser test");
-    return EXIT_FAILURE;
-  }
-
   n = mrb_compile_string(mrb, "\
 def fib(n)\n\
   if n<2\n\