test: __version__ matches package's actual version

pyproject.toml

@@ -27,6 +27,7 @@ varname = ["varname"]
 pytest = "^6.2.1"
 mypy = "^0.971"
 black = "^20.8b1"
+toml = "*"
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]

test_sentinel.py

@@ -3,6 +3,7 @@
 
 import copy
 import pickle
+from pathlib import Path
 
 import pytest
 
@@ -18,6 +19,8 @@
 # Must be defined at module-level due to limitations in how the pickle module works :/
 Pickleable = sentinel.create("Pickleable")
 
+PACKAGE_ROOT = Path(__file__).parent.resolve()
+
 
 def test_basic_usage():
     """
@@ -173,3 +176,17 @@ def test_can_get_instance_from_class():
     MySentinel = sentinel.create("MySentinel")
     MySenintelType = type(MySentinel)
     assert MySenintelType.instance is MySentinel
+
+
+def test_version_number():
+    """
+    Ensure the version number in the package matches what's in the pyproject.toml.
+    """
+    import toml  # type: ignore
+
+    from sentinel import __version__ as version
+
+    config_file = PACKAGE_ROOT / "pyproject.toml"
+    assert config_file.exists()
+    pyproject = toml.load(config_file)
+    assert pyproject["tool"]["poetry"]["version"] == version