Fix install of completion if dirs missing

Fixes situations if completion directories are missing and adds tests for installer.

tests/test_completion.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+import sys
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from bdfr.completion import Completion
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="Completions are not currently supported on Windows.")
+def test_cli_completion_all(tmp_path: Path):
+    with patch("appdirs.user_data_dir", return_value=str(tmp_path)):
+        Completion("all").install()
+        assert Path.exists(Path(str(tmp_path) + "/bash-completion/completions/bdfr")) == 1
+        assert Path.exists(Path(str(tmp_path) + "/fish/vendor_completions.d/bdfr.fish")) == 1
+        assert Path.exists(Path(str(tmp_path) + "/zsh/site-functions/_bdfr")) == 1
+        Completion("all").uninstall()
+        assert Path.exists(Path(str(tmp_path) + "/bash-completion/completions/bdfr")) == 0
+        assert Path.exists(Path(str(tmp_path) + "/fish/vendor_completions.d/bdfr.fish")) == 0
+        assert Path.exists(Path(str(tmp_path) + "/zsh/site-functions/_bdfr")) == 0
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="Completions are not currently supported on Windows.")
+def test_cli_completion_bash(tmp_path: Path):
+    with patch("appdirs.user_data_dir", return_value=str(tmp_path)):
+        Completion("bash").install()
+        assert Path.exists(Path(str(tmp_path) + "/bash-completion/completions/bdfr")) == 1
+        Completion("bash").uninstall()
+        assert Path.exists(Path(str(tmp_path) + "/bash-completion/completions/bdfr")) == 0
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="Completions are not currently supported on Windows.")
+def test_cli_completion_fish(tmp_path: Path):
+    with patch("appdirs.user_data_dir", return_value=str(tmp_path)):
+        Completion("fish").install()
+        assert Path.exists(Path(str(tmp_path) + "/fish/vendor_completions.d/bdfr.fish")) == 1
+        Completion("fish").uninstall()
+        assert Path.exists(Path(str(tmp_path) + "/fish/vendor_completions.d/bdfr.fish")) == 0
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="Completions are not currently supported on Windows.")
+def test_cli_completion_zsh(tmp_path: Path):
+    with patch("appdirs.user_data_dir", return_value=str(tmp_path)):
+        Completion("zsh").install()
+        assert Path.exists(Path(str(tmp_path) + "/zsh/site-functions/_bdfr")) == 1
+        Completion("zsh").uninstall()
+        assert Path.exists(Path(str(tmp_path) + "/zsh/site-functions/_bdfr")) == 0