testing-worksheet-python.qmd

---
title: "Testing in Python worksheet"
format: html
---

Welcome to the testing in R worksheet! This is designed to give you some hands-on practice with testing syntax in R. Run the cell below to load the libraries needed for this worksheet, and to check your answers as you go!

```{python}
import pytest
```

### Exercise 1

*Solution posted at end of worksheet.*

Write a function called `mpg_to_kml` that takes a vector of numbers in miles per gallon units and converts it to a vector in kilometeres per litre.

*Hint: 1 mile per gallon is 0.425144 kilometres per litre.*

```{python}
def mpg_to_kml():
  pass

#mpg_to_kml(1)
```

### Exercise 2

*Solution posted at end of worksheet.*

Write **at least** two assertions inside of test function to ensure that your function works as expected (i.e., do you get back expected values given your input values - is the math correct?).

*Hint: test edge cases that you can compute by hand, and be sure of your answer!*

<img src="img/unit-tests.png" width="350"/>

*Source: Austin Powers + http://www.quickmeme.com/meme/3ua14n*

```{python}
# YOUR CODE HERE
```

### Exercise 3

*Solution posted at end of worksheet.*

Add one or more exceptions to your `mpg_to_kml` function so that you can handle inappropriate user input, such as strings, lists or numpy arrays.

<img src="img/fail-you-will-fail-fast-you-should.jpg" width="300"/>

*Source: Star Wars + https://memegenerator.net/*

### Exercise 4

*Solution posted at end of worksheet.*

Now write **at least** two assertions inside of a test function to ensure that your function fails as expected (i.e., does your function throw errors when incorrect inputs are given?).

```{python}
# YOUR CODE HERE
```

### Exercise 5

*Solution posted at end of worksheet.*

Now numpy style docstring documentation for your function!

```{python}
# YOUR CODE HERE
```

## Solutions

### Exercise 1 solution

```         
def: mpg_to_kml(x):
    return x * 0.425144
```

### Exercise 2 solution

```         
def test_mpg_to_kml():
    '''Should return expected values from converting miles to gallon 
    to kilometers to litres.'''
    assert mpg_to_kml(1) == pytest.approx(0.425144)
    assert mpg_to_kml(2) == pytest.approx(0.850288)
    assert mpg_to_kml(1) == pytest.approx(4.25144) 
```

### Exercise 3 solution

```         
def mpg_to_kml(x):
    if not isinstance(x, (int, float)):
        raise ValueError("Input must be a number.")
    return x * 0.425144
```

### Exercise 4 solution

```
def test_mpg_to_kml():
    '''Should throw exceptions when strings or lists are given as input.'''         
    with pytest.raises(ValueError):
        mpg_to_kml("a")

    with pytest.raises(ValueError):
        mpg_to_kml([10, 20, 30])  
```

### Exercise 5 solution

Numpy style docstring documentation only:

```         
    """
    Convert miles per gallon to kilometers per liter.

    Parameters
    ----------
    mpg : float or int
        Fuel efficiency in miles per gallon.

    Returns
    -------
    float
        Fuel efficiency in kilometers per liter.

    Raises
    ------
    ValueError
        If the input is not a scalar (integer or float).

    Examples
    --------
    >>> mpg_to_kml(10)
    4.25144

    >>> mpg_to_kml(25)
    10.6286
    """
```