add dummy tests

we need to have some tests at first to setup pytest,tox and ci

Author: aahnik

tests/__init__.py

@@ -0,0 +1,7 @@
+from s_tool import __version__
+
+
+def test_version():
+    # a dummy test, for setting up pytest, tox, and test on ci
+    # will remove it after writing real test cases
+    assert __version__.startswith("0")

tests/test_version.py

@@ -0,0 +1,9 @@
+[tox]
+isolated_build = True
+envlist = py38,py39
+
+[testenv]
+deps =
+    pytest
+    pytest-cov
+commands = pytest