diff --git a/dev_requirements.in b/dev_requirements.in
index 5ac72d3..b399c9f 100644
--- a/dev_requirements.in
+++ b/dev_requirements.in
@@ -1,6 +1,7 @@
-black
-flake8
-invoke
-pip-tools
-pre-commit
-pylint
+black==22.8.0
+flake8==5.0.4
+invoke==1.7.1
+pip-tools==6.8.0
+pre-commit==2.20.0
+pylint==2.15.2
+pytest==7.1.3
diff --git a/dev_requirements.txt b/dev_requirements.txt
index 13dc905..a46f984 100644
--- a/dev_requirements.txt
+++ b/dev_requirements.txt
@@ -6,6 +6,8 @@
 #
 astroid==2.12.9
     # via pylint
+attrs==22.1.0
+    # via pytest
 black==22.8.0
     # via -r dev_requirements.in
 build==0.8.0
@@ -26,6 +28,8 @@ flake8==5.0.4
     # via -r dev_requirements.in
 identify==2.5.5
     # via pre-commit
+iniconfig==1.1.1
+    # via pytest
 invoke==1.7.1
     # via -r dev_requirements.in
 isort==5.10.1
@@ -41,7 +45,9 @@ mypy-extensions==0.4.3
 nodeenv==1.7.0
     # via pre-commit
 packaging==21.3
-    # via build
+    # via
+    #   build
+    #   pytest
 pathspec==0.10.1
     # via black
 pep517==0.13.0
@@ -53,8 +59,12 @@ platformdirs==2.5.2
     #   black
     #   pylint
     #   virtualenv
+pluggy==1.0.0
+    # via pytest
 pre-commit==2.20.0
     # via -r dev_requirements.in
+py==1.11.0
+    # via pytest
 pycodestyle==2.9.1
     # via flake8
 pyflakes==2.5.0
@@ -63,6 +73,8 @@ pylint==2.15.2
     # via -r dev_requirements.in
 pyparsing==3.0.9
     # via packaging
+pytest==7.1.3
+    # via -r dev_requirements.in
 pyyaml==6.0
     # via pre-commit
 toml==0.10.2
@@ -71,8 +83,8 @@ tomli==2.0.1
     # via
     #   black
     #   build
-    #   pep517
     #   pylint
+    #   pytest
 tomlkit==0.11.4
     # via pylint
 typing-extensions==4.3.0
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29