Fetch and compile test deps.

Makefile

@@ -18,7 +18,7 @@ update-deps:
 	@$(REBAR) update-deps
 
 .PHONY: tests
-tests: src/erlydtl_parser.erl
+tests: src/erlydtl_parser.erl | deps/eunit_formatters
 	@$(REBAR) -C rebar-tests.config eunit
 
 check: tests dialyze
@@ -70,3 +70,6 @@ shell:
 # this file must exist for rebar eunit to work
 # but is only built when running rebar compile
 src/erlydtl_parser.erl: compile
+
+deps/eunit_formatters:
+	@$(REBAR) -C rebar-tests.config get-deps compile