feat(#7): move to directory dialog

Utilities:
- list_directories

lua/obs/utils.lua

@@ -0,0 +1,23 @@
+local File = require "coredor.file"
+
+local M = {}
+
+function M.list_directories(path_string)
+    if path_string == nil then
+        error "path must not be nil"
+    end
+
+    local file = File:new(path_string)
+    local plenary_file = file:as_plenary()
+
+    if not plenary_file:exists() then
+        error("path '" .. path_string .. "' must exist")
+    end
+    if not plenary_file:is_dir() then
+        error(
+            "path '" .. path_string .. "' must point to directory, not a file"
+        )
+    end
+end
+
+return M

lua/obs/utils_spec.lua

@@ -0,0 +1,30 @@
+local spec = require "coredor.spec"
+local coredor = require "coredor"
+
+describe("list directories", function()
+    local utils = require "obs.utils"
+    local list_directories = utils.list_directories
+    local temp_file_fixture = spec.temp_file_fixture()
+
+    it("nil parameter causes error", function()
+        assert.has_error(function()
+            list_directories()
+        end, "path must not be nil")
+    end)
+
+    it("not existing directory causes error", function()
+        local invalid_directory_path = "invalid directory " .. coredor.uuid()
+
+        assert.has_error(function()
+            list_directories(invalid_directory_path)
+        end, "path '" .. invalid_directory_path .. "' must exist")
+    end)
+
+    it("not directory causes error", function()
+        local file_path = temp_file_fixture.path
+
+        assert.has_error(function()
+            list_directories(file_path)
+        end, "path '" .. file_path .. "' must point to directory, not a file")
+    end)
+end)