diff --git a/src/python_package/__init__.py b/src/python_package/__init__.py
index 851aa6a..c0a0890 100644
--- a/src/python_package/__init__.py
+++ b/src/python_package/__init__.py
@@ -4,8 +4,8 @@
 
 __version__ = metadata.version("python_package")
 
-from .mockup import hello_world
+from .mockup import hello_world, saved_world
 
 # The __all__ variable is a list of variables which are imported
 # when a user does "from example import *"
-__all__ = ["hello_world"]
+__all__ = ["hello_world", "saved_world"]
diff --git a/src/python_package/mockup.py b/src/python_package/mockup.py
index d8232c6..4b39c12 100644
--- a/src/python_package/mockup.py
+++ b/src/python_package/mockup.py
@@ -13,5 +13,33 @@ def hello_world(n: int) -> str:
     -------
     str
         str of 'hello world' n-times
+
+    Examples
+    --------
+    >>> hello_world(3)
+    'hello world hello world hello world'
     """
     return " ".join(repeat("hello world", n))
+
+
+def saved_world(filename: str) -> int:
+    """
+    Count how many times 'hello world' is in a file.
+
+    Parameters
+    ----------
+    filename : str
+        The file to read
+
+    Returns
+    -------
+    int
+        How many times 'hello world' is in the file
+
+    Examples
+    --------
+    >>> saved_world("not-real.txt") # doctest: +SKIP
+    """
+    with open(filename, "r") as f:
+        content = f.read()
+    return content.count("hello world")
diff --git a/tests/README.md b/tests/README.md
new file mode 100644
index 0000000..3207159
--- /dev/null
+++ b/tests/README.md
@@ -0,0 +1,112 @@
+---
+marp: true
+theme: uncover
+paginate: true
+backgroundColor: #fff
+---
+
+# **Getting started with pytesting**
+
+---
+
+## Quick start
+
+### Installation
+
+Install pytest. e.g., from the "dev" dependencies
+
+```bash
+pip install ".[dev]"
+```
+
+### How to use
+
+To execute the tests run e.g.
+
+```bash
+pytest
+```
+
+---
+
+## Test development tips
+
+---
+
+### Folder and test naming
+
+1. The tests for functions in `<filename>.py` should go in `tests/test_<filename>.py`
+
+   e.g., the tests for [python_package/mockup.py](../src/python_package/mockup.py) are in [tests/test_mockup.py](test_mockup.py)
+
+2. The test names should start with `def test_<corresponding_function_name> ...`
+
+   e.g., `def test_hello_world(): ...`
+
+---
+
+### Some Pytest decorators
+
+1. To indicate that the test function is expected to fail you can prepend
+
+   ```python
+   @pytest.mark.xfail(raises=TypeError)
+   def test_hello_world_str(): ...
+   ```
+
+---
+
+2. To setup and cleanup any resources for a test you can use [pytest fixtures with `yield`](https://dev.to/dawidbeno/understanding-yield-in-pytest-fixtures-4m38)
+
+   ```python
+   @pytest.fixture
+   def temp_file():
+       # set up
+       < code to create a file>
+       # return
+       yield
+           the_file
+       # clean up
+       < code to remove the file>
+   ```
+
+---
+
+### Doctests
+
+You can also include tests in your docstrings using `>>>` followed by the expected result e.g.
+
+```python
+def hello_world(n):
+    """
+    Prints 'hello world' n-times.
+        ...
+
+    Examples
+    --------
+    >>> hello_world(3)
+    'hello world hello world hello world'
+        ...
+    """
+```
+
+Needs `addopts = --doctest-modules` in `pytest.ini` in root of directory
+
+---
+
+### Skipping in doctests
+
+If you know that the test cannot succeed but would like to include an example usage in the docstring still then you can add `# doctest: +SKIP` e.g.
+
+```python
+def saved_world(filename):
+    """
+    Count how many times 'hello world' is in a file.
+        ...
+
+    Examples
+    --------
+    >>> saved_world("not-real.txt") # doctest: +SKIP
+        ...
+    """
+```
diff --git a/tests/test_mockup.py b/tests/test_mockup.py
index 80ebb89..9307ed3 100644
--- a/tests/test_mockup.py
+++ b/tests/test_mockup.py
@@ -1,7 +1,31 @@
-from python_package import hello_world
+from python_package import hello_world, saved_world
+import pytest
 
 
 def test_hello_world_3times():
     expected = "hello world hello world hello world"
     result = hello_world(3)
     assert result == expected
+
+
+@pytest.mark.xfail(raises=TypeError)
+def test_hello_world_str():
+    hello_world("3")
+
+
+@pytest.fixture
+def temp_file():
+    # set up
+    filename = "temp_hellooo.txt"
+    with open(filename, "w") as f:
+        f.write("hello world hello world hello world")
+    yield filename
+    # clean up
+    import os
+
+    os.remove(filename)
+
+
+def test_saved_world_3times(temp_file):
+    result = saved_world(temp_file)
+    assert result == 3