“	You CANNOT be my super-genius twin sister.	„
	~ Susan reacting in disbelief while arguing with Mary in "Johnny to the Center of the Earth".

Susannah Laura "Susan" Test is the younger twin sister of Mary Test . She is one of the two tritagonists of the series and the older sister of Johnny Test.

Characteristics

Susan is a super genius scientist and the younger twin sister of Mary (both being 13) as she is tomboyish and firm as her brother Johnny, but like her sister, Susan cherishes a deep love and obsession for Gil.

Bling-Bling Boy (a.k.a Eugene) has a crush on Susan and won over her heart after eating his energy bar in the episode “Phat Johnny”. It made him extremely muscular and was able to get a date with Susan winning her over with his charm. Like her sister, she attends school at the Porkbelly Institute of Technology. Susan is prone to believing in the more scientific and logical explanations for things rather than the illogical and magical explanations. Her sister is more open-minded, and Mary is frequently proven correct. Susan seems to be less open-minded than her twin Mary and tends to be less conservative, as she speaks her mind much more often she 1 minutes younger than her twin sister Mary

Relationships

Gil

Like her sister Mary, Susan is head over heels for Gil. She did things with Mary from watching him from a satellite in their lab and trying to hang out with him. Despite living next door to the girls for most of his life, Gil often forgets them, much to their dismay.

Johnny

Susan is Johnny's sister and generally assists Johnny and Dukey with their creative inventions. For some reason, she gets annoyed by Johnny and is more likely to explode at him whenever his antics get under her nerves, but she still loves Johnny as a brother.

Hugh

Susan loves her father but despises his meatloaf and his constant punishments for doing experiments and studying them on Johnny.

Lila

Lila and Susan seem to have a good mother-daughter bonding.

Dukey

For some reasons, Dukey truly annoys Susan, but he still has respect for her as she's one of his owners.

Bling Bling Boy

Bling Bling Boy has a crush on Susan. However, she does not share the same feelings of love and regards him as an annoyance.

Appearance and Design

Susan has pale skin, and very long straight red hair, blue eyes, and wears square glasses. She wears a pastel blue shirt with a blue star on it, a black skirt and white socks with black Mary Jane shoes and a lab coat. She wears a star-shaped hair clip.

For formal occasions, she typically wears a purple dress with a black choker and flats.

Her swimwear consists of a light blue one-piece swimsuit with a keyhole exposing her backside, and light-blue sandals.

Trivia

• Susan's counterpart in Leadbelly is named Simon West, although the colors on Simon's shirt are reversed.
• Susan and Mary's catchphrase is "We're such geniuses."
• Susan and Mary's creepy crush on Gil was actually inspired by the real life crimes of Chris Savino, who was the show's producer and director during season one.
• She and Mary are extremely ticklish, as was revealed in the episode "Johnny vs. The Tickler".
• She and Mary are revealed to suffer from plantar hyperhidrosis, "stinky feet", in "Johnny Unplugged".
• Susan has a bigger temper than Mary, similar to her mother's.
• The Quantum of Johnny and Future Johnny are the only episodes she doesn't appear in.
• Susan's name is inspired by the word star as star starts with the letter s, she wears a star-shaped hairclip and a shirt with a star on it.
• While never outright stated, since both Susan and Mary wish to marry Gil, it implies both are aware of the concept of polygamy (a multi-person relationship) and are fine with being co-wives. Considering their genius, it's not like they would be ignorant of something like this.
• Though never officially stated, it could be suggested that her first name was taken from the “Invisible Woman” from Marvel’s Fantastic 4, as they both are incredibly smart, but also have a younger brother (who also happen to share the same name), and had similar powers in the episode JX4.
• The Netflix revival changed her eye color to teal, to match Mary's.

Quotes

"You cannot be my prodigy genius twin sister!" "Now hold still, this won't hurt a bit, it's gonna hurt a lot."