Fix handling of multiple test files

Test files were sourced sequentially, but their test cases persisted
causing them to be run more than once. Instead, run each test file in a
separate Vim session.

Author: axelf4

Makefile

@@ -9,6 +9,6 @@ endif
 all: check
 
 check:
-	$(VIM) --clean $(args) -u runtest.vim
+	$(foreach test,$(wildcard test/*.vim),$(VIM) --clean $(args) -u runtest.vim "$(test)")
 
 .PHONY: all check

runtest.vim

@@ -1,31 +1,28 @@
+let s:testfile = expand('%')
 let s:has_errors = 0
 
 try
 	execute 'cd' fnamemodify(resolve(expand('<sfile>:p')), ':h')
-	execute 'source' 'plugin/strip_trailing_whitespace.vim'
+	source plugin/strip_trailing_whitespace.vim
 
-	let s:testfiles = glob('test/*.vim', 1, 1)
-	for s:testfile in s:testfiles
-		execute 'source' s:testfile
-
-		let s:tests = map(split(execute('function /^Test_'), "\n"), {_, v -> matchstr(v, 'function \zs\k\+\ze()')})
-		for s:test_function in s:tests
-			let v:errors = []
-			try
-				echo 'Test' s:test_function
-				execute 'call' s:test_function '()'
-			catch
-				call add(v:errors, "Uncaught exception in test: " .. v:exception .. " at " .. v:throwpoint)
-			finally
-				if !empty(v:errors)
-					echo s:testfile .. ':1:Error'
-					for s:error in v:errors
-						echo s:error
-					endfor
-					let s:has_errors = 1
-				endif
-			endtry
-		endfor
+	source %
+	let s:tests = map(split(execute('function /^Test_'), "\n"), {_, v -> matchstr(v, 'function \zs\k\+\ze()')})
+	for s:test_function in s:tests
+		let v:errors = []
+		echo 'Test' s:test_function
+		try
+			execute 'call' s:test_function '()'
+		catch
+			call add(v:errors, "Uncaught exception in test: " .. v:exception .. " at " .. v:throwpoint)
+		finally
+			if !empty(v:errors)
+				echo s:testfile .. ':1:Error'
+				for s:error in v:errors
+					echo s:error
+				endfor
+				let s:has_errors = 1
+			endif
+		endtry
 	endfor
 catch
 	echo v:exception