Add tomli test case for different python versions

pyproject.toml

@@ -21,7 +21,10 @@ task = 'taskipy.cli:main'
 
 [tool.poetry.dependencies]
 python = "^3.6"
-tomli = "^1.2.3"
+tomli = [
+    { version = "^2.0.1", python = "^3.7" },
+    { version = "^1.2.3", python = "~3.6" }
+]
 psutil = "^5.7.2"
 mslex = { version = "^0.3.0", markers = "sys_platform == 'win32'" }
 colorama = "^0.4.4"

tests/test_tomli_install.py

@@ -0,0 +1,49 @@
+import subprocess
+import sys
+import unittest
+from typing import Dict, List, Tuple
+
+
+class TomliInstallTestCase(unittest.TestCase):
+    def test_correct_tomli_version_installed(self):
+        python_major, python_minor = self.__get_current_python_version()
+        packages = self.__get_installed_pip_packages()
+        tomli_version = packages.get('tomli')
+        v1_regex = r'1.[0-9]+.[0-9]+'
+        v2_regex = r'2.[0-9]+.[0-9]+'
+
+        if python_major == 3 and python_minor == 6:
+            self.assertRegex(tomli_version, v1_regex)
+        elif python_major == 3 and python_minor >= 7:
+            self.assertRegex(tomli_version, v2_regex)
+        else:
+            self.fail("Executed with invalid Python version")
+
+    def __get_current_python_version(self) -> Tuple[int, int]:
+        python_version = sys.version_info
+
+        return python_version.major, python_version.minor
+
+    def __get_installed_pip_packages(self) -> Dict[str, str]:
+        cmd = "pip list"
+        process = subprocess.Popen(
+            cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE
+        )
+        stdout, _ = process.communicate()
+        exit_code = process.returncode
+        if exit_code != 0:
+            raise RuntimeError(
+                'listing pip packages got a non-zero exit code'
+            )
+
+        result = {}
+        packages = self.__remove_pip_list_table_header(stdout.splitlines())
+        for package in packages:
+            decoded_package = package.decode('utf-8')
+            name, version = decoded_package.split()
+            result[name] = version
+
+        return result
+
+    def __remove_pip_list_table_header(self, lines: List[bytes]) -> List[bytes]:
+        return lines[2:]