Use macro per-test-file

Signed-off-by: Marcel Müller <neikos@neikos.email>

tests/cases/4-output@simple_for.snap

@@ -1,13 +0,0 @@
----
-source: tests/file_tests.rs
-expression: output
-info:
-  input: "{{ for value in values -}}\n    {{-= value }}\n{{- end }}\n{{ for value in no_values -}}\n    {{-= value }}\n{{ else -}}\nNo Values >:C\n{{- end }}"
-  context:
-    no_values: []
-    values:
-      - one
-      - two
-input_file: tests/cases/simple_for.nomo
----
-"one\ntwo\n\nNo Values >:C"