Check your understanding of the previous reading: what a unit test is, why it matters, and how to judge whether a test passes.

The first line of the following code is unnecessary:

from bakery import assert_equal

def days_to_hours(days: int) -> int:
    return 24 * days

assert_equal(days_to_hours(2), 24)

Select one answer, then check.

True
Not quite. Without that import, assert_equal would not exist and the last line would crash.
False
Correct. The last line calls assert_equal, which only exists because the first line imported it.

A unit test is:

Select one answer, then check.

A collection of known inputs and outputs for a function.
Correct. A unit test calls a function with a known input and compares the result to a known output.
A conditional that determines whether the units (e.g., inches, gallons) are correct.
Not quite. "Unit" here means a small, isolated piece of code (like one function), not a unit of measurement.
A function that returns a Boolean value.
Not quite. A unit test is a check on a function, not simply any function that returns True or False.
A function that consumes a function and returns whether the function is correct.
Not quite. assert_equal checks one known input/output pair; it does not analyze the function's code.

Given this function, which of the following unit tests will pass?

from bakery import assert_equal

def simple_formula(x: int) -> int:
    return 3 * x + 4

Select every answer that applies, then check.

assert_equal(simple_formula(0), 4)
Passes. 3 * 0 + 4 is 4.
assert_equal(simple_formula(3), 13)
Passes. 3 * 3 + 4 is 13.
assert_equal(simple_formula(-.5), 2.5)
Passes. 3 * -0.5 + 4 is 2.5; Python does not enforce the int type hint at runtime.
assert_equal(simple_formula(0), 0)
Fails. simple_formula(0) is 4, not 0.
assert_equal(simple_formula(-1), 2)
Fails. 3 * -1 + 4 is 1, not 2.
assert_equal(simple_formula(0:int)->int, 0: int)
Fails — this is not valid Python at all; a type annotation cannot appear inside a function call.

Which of the following are advantages of unit tests?

Select every answer that applies, then check.

They help you find problems early.
Correct — one of the three advantages from the reading.
They help you facilitate changes down the road.
Correct — one of the three advantages from the reading.
They make it easier to glue together pieces of code.
Correct — one of the three advantages from the reading.
They make your code easier to read.
Not a stated advantage. Unit tests are separate code, alongside the function; they don't change how readable the function itself is.
They make your code run faster.
Not an advantage. Running the tests takes extra time; they don't speed up the program itself.

When someone says, "My program looks correct, but it says it fails the unit tests."

Select one answer, then check.

The program is probably not correct.
Correct. Looking correct is not the same as being correct — trust what the tests report.
The program is probably correct.
Not quite. If a program fails its unit tests, something the programmer expected does not actually hold.

How many unit tests should a program have?

Select one answer, then check.

As many as it takes
Correct. The reading gives no fixed number — enough tests to be valid and thorough, which varies by function.
1
Not quite. A single test is rarely thorough enough to catch every incorrect implementation.
5
Not quite. There is no fixed number — it depends on the function being tested.
100
Not quite. There is no fixed number — it depends on the function being tested.
One for each line of code
Not quite. Tests are written per scenario, not per line — a single test line can exercise several lines of code.