Add shellcheck tests

Makefile

@@ -14,9 +14,26 @@ pdf:
 	@rm yadm.ps
 
 .PHONY: test
-test:
+test: bats shellcheck
+
+.PHONY: bats
+bats:
+	@echo Running all bats tests
 	@bats test
 
+.PHONY: shellcheck
+shellcheck:
+	@echo Running shellcheck
+	@shellcheck --version || true
+	@shellcheck -s bash yadm test/*.bash
+	@for bats_file in test/*bats; do \
+		sed 's/^@test.*{/function test() {/' "$$bats_file" > "$$bats_file .bash"; \
+		shellcheck -s bash "$$bats_file .bash"; \
+		test_result="$$?"; \
+		rm -f "$$bats_file .bash"; \
+		[ "$$test_result" -ne 0 ] && exit 1; \
+	done; true
+
 man:
 	groff -man -Tascii ./yadm.1 | less