Basic command-line calculator
Naming
Adhere to the Java Naming Conventions.

Names of methods and variables start with a lowercase letter, names of classes with an uppercase letter.

Method names should start with a verb so that they read like an instruction. Names of variables should start with a noun.

Exception to that are variables holding or methods returning a boolean which both should start with is, can, has or alike.


Don't surprise your readers
You have a variable named numberTest but it does not contain a test for a number but the current operation or the users choice.
Code Quality
Structure  your code with methods.
You wrote a single long method.
This method contains an if/else cascade that somehow separates the method in to different sections.
You should extract this blocks in to separate Methods (leaving the if/else instructions in main) so that the main method becomes shorter and easier to read (and to maintain).
Don't repeat yourself
All over your code you repeat this two lines with varying variable names:
            System.out.println(questionSix);
            double number2 = scan.nextDouble();

This two lines could be extracted to a separate method that takes the String as parameter and returns the double value. That would shrink four lines in your code to just one.