Implement testing with existing tests

The code that's being removed here made no sense. It is a `check`
rule, and it did the following things:

1. For every `.el` file it was searching its `tests.el` counterpart.
    Which doesn't exist.

2. It was checking the correctness of `declare-function`s. Which would
    be fine, wasn't it for the fact the project has zero
    `declare-function`s.
3. It was checking that `ert` exists, which it does on all supported
    Emacs versions.
4. It was removing .elc files before running the tests. Why? 🤷‍♂️

Replace everything with a single `test` rule which simply loads the
test files and runs the tests.

Besides being actually useful, this also improves running time as:

    Initial state | Before | After |
    Non-compiled  | 2.177  | 0.340 |
    Compiled      | 2.182  | 1.614 |

.github/workflows/ci.yml

@@ -29,4 +29,4 @@ jobs:
 
     - uses: actions/checkout@v2
     - name: Run tests
-      run: make check
+      run: make test

Makefile

@@ -23,43 +23,31 @@ ELFILES = \
 	purescript-unicode-input-method.el \
 	purescript-utils.el \
 	purescript-decl-scan.el \
-	purescript-yas.el
+	purescript-yas.el \
+	tests/purescript-sort-imports-tests.el \
+	tests/purescript-str-tests.el
 
 ELCFILES = $(ELFILES:.el=.elc)
 AUTOLOADS = purescript-mode-autoloads.el
 
 PKG_DIST_FILES = $(ELFILES) logo.svg NEWS purescript-mode.info dir
 PKG_TAR = purescript-mode-$(VERSION).tar
-ELCHECKS=$(addprefix check-, $(ELFILES:.el=))
 
 %.elc: %.el
 	@$(BATCH) \
 	   --eval "(setq byte-compile-error-on-warn t)" -f batch-byte-compile $<
 
-.PHONY: all compile info clean check $(ELCHECKS) elpa package
+.PHONY: all compile info clean test elpa package
 
 all: compile $(AUTOLOADS) info
 
 compile: $(ELCFILES)
 
-$(ELCHECKS): check-%: %.el
-	@$(BATCH) --eval '(when (check-declare-file "$*.el") (error "check-declare failed"))'
-	@$(BATCH) \
-		 --eval "(setq byte-compile-error-on-warn t)" \
-		 -f batch-byte-compile $*.el
-	@$(RM) $*.elc
-	@if [ -f "$(<:%.el=tests/%-tests.el)" ]; then \
-	if $(BATCH) --eval "(require 'ert)" 2> /dev/null; then \
-		echo; \
-		$(BATCH) -l "$(<:%.el=tests/%-tests.el)" -f ert-run-tests-batch-and-exit; \
-	else \
-		echo "ERT not available, skipping unit tests"; \
-	fi; \
-	fi
-	@echo "--"
-
-check: clean $(ELCHECKS)
-	@echo "checks passed!"
+test: compile
+	@$(BATCH) -l tests/purescript-sort-imports-tests.elc \
+		-l tests/purescript-str-tests.elc \
+		-f ert-run-tests-batch-and-exit
+	@echo "tests passed!"
 
 clean:
 	$(RM) $(ELCFILES) $(AUTOLOADS) $(AUTOLOADS:.el=.elc) $(PKG_TAR) purescript-mode.tmp.texi purescript-mode.info dir