Move snapshot tests into separate module

tests/tests.rs

@@ -1,5 +1,6 @@
 mod tester;
 
+mod snapshot {
     use tester::BatTester;
 
     macro_rules! snapshot_tests {
@@ -39,3 +40,4 @@ snapshot_tests! {
         tabs_4:                      "full"                        => [wrap: false, tabs: 4],
         tabs_8:                      "full"                        => [wrap: false, tabs: 8],
     }
+}