Johnny Test Wiki
Mary Test
Powers and abilities Intelligence


Gender Female
Age 14
Hair Color Red
Eye Color Green
Status Alive
Aliases Test Sister, Girl that I've never seen before (by Gil), Melinda (by Gil)
Personality Intelligent, scientific, quiet, level-headed, compassionate, empathetic, kind, caring, loving, serious (when it comes to situation or confronting Johnny), sympathetic, conservative, friendly, warm-hearted, open-minded, girly, very smart, soft-spoken, ticklish
Friends Johnny Test
Susan Test
Mr. Black
Mr. White
Gil Nexdor (for some reasons)
Enemies Bling-Bling Boy
Dark Vegan
Zizrar the Mole King
Mr. Mittens
The Tickler
Evil Johnny
Alignment Good
Love Interest {{{Ben Mallet}}}
Likes Science, inventions, Gil Nexdor
Dislikes Bling Bling Boy constantly harassing her sister, Johnny being a selfish or misusing her and Susan's inventions, Susan's temper, Hugh's meat loaf, being punished.
Family Hugh Test (father)
Lila Test (mother)
Susan Test (younger twin sister)
Johnny Test (younger brother)
Pets Dukey (dog)
First Appearance Pilot Episode (originally)

Johnny to the Center of the Earth (official debut)

Voiced by Brittney Wilson(Seasons 1 & 5)
Ashleigh Ball (Seasons 2-4 & 6)
Laurie Hymes (Web Series)
Emily Tennant (Seasons 7-8)

Marrionette Louise "Mary" Test is one of the two tritagonists of Johnny Test. She is the oldest of the two twins.


Mary is a super-genius twin sister of Susan and the older sister of Johnny. Like her sister, Mary harbors affection for the next-door neighbor Gil Nexdor, and attends school at the Porkbelly Institute of Technology (a.k.a Porkbelly Tech). The two are rarely (if ever) seen acting independently of each other, and work best in unison due to their shared high IQ.

Despite their similarities, Mary is more open-minded than Susan, but much less outspoken. While Susan sticks strictly to facts and realistic science, Mary is open to more hypothetical sciences such as extraterrestrials and cryptids, which often incites Susan's skepticism. Mary is also on somewhat better terms with their brother, due to her marginally higher empathy, though she is also highly prone to following Susan's more headstrong-attitude.


Mary has long curly red hair tied in a high ponytail and green eyes inherited from her mother. Her style of dress is very casual, especially compared to her sister's preppy style. She wears a pastel yellow shirt with a moon design. blue jeans, olive green sneakers with a moon design, white lab coat and a moon hairclip. Like her sister, she requires glasses to see, but she wears stylized frames with pointed tips.

For formal occasions, she typically wears a light blue dress with a magenta belt and flats.




Mary and Susan have a strong sisterly relationship, both being geniuses with many shared goals. As twins, Mary can often read Susan's mind (like "twin telepathy"). Mary and Susan do almost anything together, like staring at Gil (their biggest crush), or supervising new experiments in their lab. However, despite their relationship, they can bicker when it comes to their differences. Being the more soft-spoken sister, Mary often lets Susan do the talking for her between the two of them.

Mary and Susan both recognize each other's desire to become Gil's boyfriend will at one point cause them to come to blows as to which of them will be the one, though they both agree to deal with this when the time comes (if ever.)



Like her sister, Mary cares for her little brother, but is not above using him as a test subject for their various experiments. Mary is however slightly more inclined to help Johnny in his various antics, shows more patience with him than Susan, and is quick to come to his aid when her sister won't. Despite this, she is just as often frustrated with Johnny's ill-thought out escapades and requests for scientific help.



Like the rest of their family, Mary loves her father, but hates his meat loaf and his constant punishments for supervising experiments.



Lila and Mary have a solid mother-daughter relationship, although the two are not seen interacting much due to the former's busy day-job and the latter's frequent lab time.


Love Interest (one sided)

Like Susan, Mary has been in love with Gil since they were all little children. The infatuation is is very surface level, as Gil is demonstrably attractive, but very short on brains and awareness, not even recognizing the twins' open infatuation with him, or that they've been neighbors since Kindergarten. Unlike Susan, Mary is more openly frustrated about Gil's lack of intellegence, and openly calls him out on this to no avail. Despite this, the twins will go to absurd lengths for Gil's attention, even if it involves forcing Gil into loving them against his will.

Bling-Bling Boy

Mary is constantly annoyed by Bling-Bling Boy's constant interruptions to her and Susan's life due to his crush on her sister, but otherwise seems to have no opinion of him. When Bling-Bling Boy was briefly brainwashed into falling in love with her instead, Mary responded with complete and utter horror.



  • Alongside Susan, her catchphrase is "We're such geniuses".
  • She and Susan are very ticklish, as was shown in "Johnny vs. The Tickler".
  • She and Susan are revealed to suffer from plantar hyperhidrosis, "stinky feet", in "Johnny Unplugged".
  • Despite being considered twins with Susan, Mary is the oldest child in the Test family.
  • So far in the series, Mary has never had any episodes primarily dedicated to her, unlike most of the other characters on the show.
  • Mary has had the most voice actor changes of any character featured in the show.
  • In Johnny's Treasure, it is stated that Mary can play the flute while Johnny and Dukey revealed she was a "Band Dork".