diff --git a/arithmetic/__init__.py b/arithmetic/__init__.py
new file mode 100644
index 0000000..dcd2470
--- /dev/null
+++ b/arithmetic/__init__.py
@@ -0,0 +1 @@
+from .operations import add
diff --git a/arithmetic/arithmetic/operations.py b/arithmetic/arithmetic/operations.py
new file mode 100644
index 0000000..60d84d6
--- /dev/null
+++ b/arithmetic/arithmetic/operations.py
@@ -0,0 +1,5 @@
+def add(a, b):
+    """
+    Return the sum of two numbers.
+    """
+    return a + b
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..e079f8a
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1 @@
+pytest
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/tests/__init__.py
@@ -0,0 +1 @@
+