fmt: add tests for gopls formatting

autoload/go/fmt_test.vim

@@ -50,6 +50,71 @@ func! Test_goimports() abort
   call assert_equal(expected, actual)
 endfunc
 
+func! Test_run_fmt_gopls() abort
+  try
+    let g:go_fmt_command = 'gopls'
+
+    let actual_file = tempname()
+    call writefile(readfile("test-fixtures/fmt/hello.go"), actual_file)
+
+    let expected = join(readfile("test-fixtures/fmt/hello_golden.go"), "\n")
+
+    " run our code
+    call go#fmt#run("gofmt", actual_file, "test-fixtures/fmt/hello.go")
+
+    " this should now contain the formatted code
+    let actual = join(readfile(actual_file), "\n")
+
+    call assert_equal(expected, actual)
+  finally
+    unlet g:go_fmt_command
+  endtry
+endfunc
+
+func! Test_update_file_gopls() abort
+  try
+    let g:go_fmt_command = 'gopls'
+
+    let expected = join(readfile("test-fixtures/fmt/hello_golden.go"), "\n")
+    let source_file = tempname()
+    call writefile(readfile("test-fixtures/fmt/hello_golden.go"), source_file)
+
+    let target_file = tempname()
+    call writefile([""], target_file)
+
+    " update_file now
+    call go#fmt#update_file(source_file, target_file)
+
+    " this should now contain the formatted code
+    let actual = join(readfile(target_file), "\n")
+
+    call assert_equal(expected, actual)
+  finally
+    unlet g:go_fmt_command
+  endtry
+endfunc
+
+func! Test_goimports_gopls() abort
+  try
+    let g:go_fmt_command = 'gopls'
+
+    let $GOPATH = 'test-fixtures/fmt/'
+    let actual_file = tempname()
+    call writefile(readfile("test-fixtures/fmt/src/imports/goimports.go"), actual_file)
+
+    let expected = join(readfile("test-fixtures/fmt/src/imports/goimports_golden.go"), "\n")
+
+    " run our code
+    call go#fmt#run("goimports", actual_file, "test-fixtures/fmt/src/imports/goimports.go")
+
+    " this should now contain the formatted code
+    let actual = join(readfile(actual_file), "\n")
+
+    call assert_equal(expected, actual)
+  finally
+    unlet g:go_fmt_command
+  endtry
+endfunc
 " restore Vi compatibility settings
 let &cpo = s:cpo_save
 unlet s:cpo_save