[tests] Make test runners exit with errorlevel 1 if a test fails.

tests/core/encoding/test_core_json.odin

@@ -3,6 +3,7 @@ package test_core_json
 import "core:encoding/json"
 import "core:testing"
 import "core:fmt"
+import "core:os"
 
 TEST_count := 0
 TEST_fail  := 0
@@ -34,6 +35,9 @@ main :: proc() {
 	marshal_json(&t)
 
     fmt.printf("%v/%v tests successful.\n", TEST_count - TEST_fail, TEST_count)
+	if TEST_fail > 0 {
+		os.exit(1)
+	}
 }
 
 @test