How to set parameters in SQLite?

I've been unable to figure out how to set parameters from within SQLite. I'm mainly using it for testing, and am designing my code so that it can be ported as easily as possible to another, yet to be determined, version of SQL. Normally, I use named parameters, and when testing queries internally, I will use the syantax @varname="value". I'll provide two examples below, showing how I would like to use parameters when testing.

This first example just sets and displays a variable.

@string="Example String";
SELECT @string;

This should return the contents of the variable, in this case: example string.

In the second example, the parameter is being used as part of a condition:

@param=Dark;
SELECT Title from table;
WHERE Title= '%' || @param || '%';

This should return results like the following:

Afterdark    
Alone in the Dark
The Darkness

etc.