feat: alternate between go and test files

lua/gopher/alternate.lua

@@ -0,0 +1,44 @@
+local M = {}
+
+function M.is_test_file()
+  local file = vim.fn.expand "%"
+  if #file <= 1 then
+    vim.notify("no buffer name", vim.log.levels.ERROR)
+    return nil, false, false
+  end
+  local is_test = string.find(file, "_test%.go$")
+  local is_source = string.find(file, "%.go$")
+  return file, (not is_test and is_source), is_test
+end
+
+function M.alternate()
+  local file, is_source, is_test = M.is_test_file()
+  if not file then
+    return nil
+  end
+  local alt_file = file
+  if is_test then
+    alt_file = string.gsub(file, "_test.go", ".go")
+  elseif is_source then
+    alt_file = vim.fn.expand "%:r" .. "_test.go"
+  else
+    vim.notify("not a go file", vim.log.levels.ERROR)
+  end
+  return alt_file
+end
+
+function M.switch(bang, cmd)
+  local alt_file = M.alternate()
+  if not vim.fn.filereadable(alt_file) and not vim.fn.bufexists(alt_file) and not bang then
+    vim.notify("couldn't find " .. alt_file, vim.log.levels.ERROR)
+    return
+  elseif #cmd <= 1 then
+    local ocmd = "e " .. alt_file
+    vim.cmd(ocmd)
+  else
+    local ocmd = cmd .. " " .. alt_file
+    vim.cmd(ocmd)
+  end
+end
+
+return M