# How can I write unit tests against code that uses Matplotlib?

To write unit test cases against a code, we can consider a plot that takes an array as x points and plot it as y=x^2. While testing, we would extract y_data for x data points.−

## Steps

• Create a method, i.e., plot_sqr_curve(x) to plot x and x^2 using plot() method and return the plot.
• To test, use unittest.TestCase.
• Write test_curve_sqr_plot() method that includes the following statements.
• Create data points for x to plot the curve.
• Using the above x data points, create y data points.
• Using x and y data points, plot the curve.
• Using pt (from step 5), extract x and y data.
• Check whether the given expression is true or not.

## Example

import unittest
import numpy as np
from matplotlib import pyplot as plt
def plot_sqr_curve(x):
"""
Plotting x points with y = x^2.
"""
return plt.plot(x, np.square(x))
class TestSqrCurve(unittest.TestCase):
def test_curve_sqr_plot(self):
x = np.array([1, 3, 4])
y = np.square(x)
pt, = plot_sqr_curve(x)
y_data = pt.get_data()[1]
x_data = pt.get_data()[0]
self.assertTrue((y == y_data).all())
self.assertTrue((x == x_data).all())
if __name__ == '__main__':
unittest.main()

## Output

Ran 1 test in 1.587s
OK