Simplify the code for most linters and tests with closures

autoload/ale/assert.vim

@@ -54,9 +54,14 @@ function! ale#assert#Linter(expected_executable, expected_command) abort
         endif
     else
         let l:command = ale#linter#GetCommand(l:buffer, l:linter)
+    endif
+
+    if type(l:command) is v:t_string
         " Replace %e with the escaped executable, so tests keep passing after
         " linters are changed to use %e.
         let l:command = substitute(l:command, '%e', '\=ale#Escape(l:executable)', 'g')
+    else
+        call map(l:command, 'substitute(v:val, ''%e'', ''\=ale#Escape(l:executable)'', ''g'')')
     endif
 
     AssertEqual
@@ -126,7 +131,9 @@ function! ale#assert#SetUpLinterTest(filetype, name) abort
 
     execute 'runtime ale_linters/' . a:filetype . '/' . a:name . '.vim'
 
-    call ale#test#SetDirectory('/testplugin/test/command_callback')
+    if !exists('g:dir')
+        call ale#test#SetDirectory('/testplugin/test/command_callback')
+    endif
 
     command! -nargs=+ WithChainResults :call ale#assert#WithChainResults(<args>)
     command! -nargs=+ AssertLinter :call ale#assert#Linter(<args>)
@@ -140,14 +147,33 @@ function! ale#assert#TearDownLinterTest() abort
     unlet! g:ale_create_dummy_temporary_file
     let s:chain_results = []
 
-    delcommand WithChainResults
-    delcommand AssertLinter
-    delcommand AssertLinterNotExecuted
-    delcommand AssertLSPOptions
-    delcommand AssertLSPLanguage
-    delcommand AssertLSPProject
+    if exists(':WithChainResults')
+        delcommand WithChainResults
+    endif
 
-    call ale#test#RestoreDirectory()
+    if exists(':AssertLinter')
+        delcommand AssertLinter
+    endif
+
+    if exists(':AssertLinterNotExecuted')
+        delcommand AssertLinterNotExecuted
+    endif
+
+    if exists(':AssertLSPOptions')
+        delcommand AssertLSPOptions
+    endif
+
+    if exists(':AssertLSPLanguage')
+        delcommand AssertLSPLanguage
+    endif
+
+    if exists(':AssertLSPProject')
+        delcommand AssertLSPProject
+    endif
+
+    if exists('g:dir')
+        call ale#test#RestoreDirectory()
+    endif
 
     Restore