Test Driven Development


Teaching: 10 min
Exercises: 30 min
  • How can figure out what my code is supposed to do?

  • How can I stay focused on building what I actually need to?

  • Define test-driven development and explain the rationale for it.

  • Write unit tests to define what what a simple function is supposed to do.

First, the Tests

  1. Using assert statements, write half a dozen tests for each of the following functions.
  2. Compare your tests to those written by your neighbors. What errors did they test for that you didn’t? What would your tests catch that they missed?
  3. Where did you interpret requirements differently? I.e., where would a function pass one of your neighbors’ tests but fail one of yours or vice versa?
Non-Decreasing Sub-Lists
Given a list of numbers, return a list of the sums of each non-decreasing sub-list. For example, if the input is [1, 2, 3, 3, 1, 5, 6, 3, 1, 2, 3], the output should be [9, 12, 3, 6].
Rectangle Overlay
Given two rectangles, each defined by the four values [x0, y0, x1, y1], return the rectangle representing their overlap. Assume all coordinates are integer. For example, if the inputs are [0, 0, 2, 2] and [1, 1, 5, 3], the output should be [1, 1, 2, 2].

Key Points

  • Test-driven development (TDD) is the practice of writing tests before writing code.

  • Writing tests first helps clarify the intent and interface of the code to be written.

  • Empirical evidence for TDD’s benefits is unclear, but many programmers find it very useful.