Alright I got you.
After reading the guide I understand you completely.
I am sorry for being rude and impulsive.
However I do not think my solution is illusory 
But just to clear things up, I screwed up writing my question pretty terribly yesterday, I admit that... What I meant by "tolerance" was stupidly enough the forward voltage. Which in this case was close to "perfection", as the typical value was for each diode is 3.2V, 0.1V off the 3.3V each arduino "number pinhole". And while each "number pinhole" can give up to 50mA, one led needs just 20 mA to light up. And as I have understood by searching on the web, a device (in this case the leds) will not use more electric current than it needs. If I would have used red leds though, I would have needed to use resistors as you say, since they have a lesser forward voltage. And so the tester basically works the way I want it too, I can see that my T-split's pinouts are not broken, as all the leds light up when the code I have below instructs them to and it also works when I rewrite the code so that just some of the leds light up.
int led1 = 13;
int led2 = 12;
int led3 = 11;
int led4 = 10;
int led5 = 9;
int led6 = 8;
int led7 = 7;
int led8 = 6;
int led9 = 5;
int led10 = 4;
void setup() {
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
pinMode(led3, OUTPUT);
pinMode(led4, OUTPUT);
pinMode(led5, OUTPUT);
pinMode(led6, OUTPUT);
pinMode(led7, OUTPUT);
pinMode(led8, OUTPUT);
pinMode(led9, OUTPUT);
pinMode(led10, OUTPUT);
}
void loop() {
digitalWrite(led1, HIGH);
digitalWrite(led2, HIGH);
digitalWrite(led3, HIGH);
digitalWrite(led4, HIGH);
digitalWrite(led5, HIGH);
digitalWrite(led6, HIGH);
digitalWrite(led7, HIGH);
digitalWrite(led8, HIGH);
digitalWrite(led9, HIGH);
digitalWrite(led10, HIGH);
In the picture named "forum1" the code above is uploaded and all ten leds are lit.
In the other picture named "forum2" I rewrote the code so that just led 1-3 are lit.
But truly thanks for your help guys.
