Implement some helpful testing types and traits in the moves package

moves/tests/pushes.rs

@@ -1,10 +1,10 @@
 // Eryn Wells <eryn@erynwells.me>
 
 use chessfriend_core::{piece, Square};
-use chessfriend_moves::{Builder, BuilderError};
+use chessfriend_moves::{testing::*, Builder};
 
 #[test]
-fn pawn_push() -> Result<(), BuilderError> {
+fn pawn_push() -> TestResult {
     let mv = Builder::push(&piece!(White Pawn on A3))
         .to(Square::A4)
         .build()?;