feat(tests): work-in-progress writing page

Author: amyheather

pages/verification_validation/tests.qmd

@@ -2,6 +2,8 @@
 title: ❌ Tests
 ---
 
+{{< include ../../scripts/_reticulate-setup.md >}}
+
 :::: {.pale-blue}
 
 **Learning objectives:**
@@ -18,7 +20,28 @@ TODO
 
 **Required packages:**
 
-TODO
+These should be available from environment setup in the "Test yourself" section of [Environments](../setup/environment.qmd). 
+
+::: {.python-content}
+
+```{python}
+import numpy as np
+import pandas as pd
+import simpy
+from sim_tools.distributions import Exponential
+import pytest
+```
+
+:::
+
+::: {.r-content}
+
+```{r}
+#| output: false
+library(simmer)
+```
+
+:::
 
 ::::
 
@@ -28,6 +51,120 @@ TODO
 3. github repo > settings > secrets and variables > actions > new token and copy in the info
 4. run workflow -->
 
+<br>
+
+Testing is the process of evaluating a model to ensure it works as expected, gives reliable results, and can handle different conditions. By **systematically checking for errors, inconsistencies, or unexpected behaviors**, testing helps improve the quality of a model, catch errors and prevent future issues.
+
+When you create a model, you will naturally carry out tests, with simple manual checks where you observe outputs and ensure they look right. These checks can be formalised and **automated** so that you can run them after any changes, and catch any issues that arise.
+
+## Introduction to writing and running tests
+
+<div class="h3-tight"></div>
+
+:::: {.python-content}
+
+### Writing a basic test
+
+A popular framework for testing in python is **pytest**.
+
+Each test in pytest is a function that contains an assertion statement to check a condition (e.g., `number > 0`). If the condition fails, pytest will return an error message (e.g. "The number should be positive").
+
+Test are typically stored in a folder called `tests/`, and filenames start with the prefix `test_`. This naming convention allows pytest to automatically discover and run all the tests in the folder.
+
+Here's an example of a simple test using pytest:
+
+```{python}
+def test_positive():
+    """
+    Confirm that the number is positive.
+    """
+    number = 5
+    assert number > 0, "The number should be positive"
+```
+
+### Running tests
+
+Tests are typically run from the terminal. Commands include:
+
+* `pytest` - runs all tests.
+* `pytest tests/filename.py` - runs tests from a specific file.
+
+When you run a test, you'll see an output like this in the terminal:
+
+::: {.callout-note icon=false title="Test output:"}
+
+```{python}
+#| echo: false
+pytest.main(["tests_resources/test_example_simple.py"])
+```
+
+:::
+
+### Parametrise
+
+We can execute the same test on different parameters using `pytest.mark.parametrize`.
+
+Here's an example:
+
+```{python}
+@pytest.mark.parametrize("number", [1, 2, 3, -1])
+def test_positive_param(number):
+    """
+    Confirm that the number is positive.
+
+    Arguments:
+        number (float):
+            Number to check.
+    """
+    assert number > 0, f"The number {number} is not positive."
+```
+
+In this example, we're testing the same logic with four different values: `1`, `2`, `3`, and `-1`. The last value, `-1`, will cause the test to fail. The error message includes the failed value for easy debugging.
+
+:::{.callout-note icon=false title="Test output:"}
+
+```{python}
+#| echo: false
+pytest.main(["tests_resources/test_example_param.py"])
+```
+
+:::
+
+::::
+
+::: {.r-content}
+
+:::
+
+## Testing the model
+
+There are many different ways of categorising tests. We will focus on three types:
+
+* **Functional testing**
+* **Unit testing**
+* **Back testing**
+
+### Functional tests
+
+Functional tests verify that the system or components perform their intended functionality.
+
+For example, we expect that the mean wait time for a doctor should decrease if:
+
+* The number of doctors increases.
+* The patient inter-arrival time increases (so there are fewer arrivals).
+* The length of the doctor consultation decreases.
+
+::: {.python-content}
+
+```{python}
+```
+
+:::
+
+::: {.r-content}
+
+:::
+
 ## Explore the example models
 
 <div class="h3-tight"></div>

pages/verification_validation/tests_resources/test_example_param.py

@@ -0,0 +1,13 @@
+import pytest
+
+
+@pytest.mark.parametrize("number", [1, 2, 3, -1])
+def test_positive_param(number):
+    """
+    Confirm that the number is positive.
+
+    Arguments:
+        number (float):
+            Number to check.
+    """
+    assert number > 0, f"The number {number} is not positive."

pages/verification_validation/tests_resources/test_example_simple.py

@@ -0,0 +1,6 @@
+def test_positive():
+    """
+    Confirm that the number is positive.
+    """
+    number = 5
+    assert number > 0, "The number should be positive"