Lesson test: Debugging

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Debugging

1.[3p]
Put the steps of the debugging method in order.

Cut the failing case down until only what is needed to fail remains
Make the bug happen on demand, with a written input and expected output
Make the observation and keep or discard the hypothesis
State a hypothesis specific enough to predict an observation

Show the answer

b, a, d, c

2.[3p]
A bug lies somewhere in a 1000 line region. How many checks does binary search need, at most, to reach a single line?

CorrectNot quite: 10

3.[2p]
A test passed at a release 512 commits ago and fails now. How many builds does `git bisect` need in the worst case?

CorrectNot quite: 9

4.[3p]
Why is "something is wrong with the sorting" a useless hypothesis?

It predicts no observation, so nothing you look at can confirm or kill it

Correct

It names the wrong part of the program

The answer is: It predicts no observation, so nothing you look at can confirm or kill it

Sorting is rarely the cause of a bug

The answer is: It predicts no observation, so nothing you look at can confirm or kill it

It should be written as a question

The answer is: It predicts no observation, so nothing you look at can confirm or kill it

5.[3p]
A bug appears only sometimes, on the same input. What does intermittency usually mean?

The program depends on something other than its input: time, randomness, ordering, or state left over from a previous run

Correct

The machine is faulty

The answer is: The program depends on something other than its input: time, randomness, ordering, or state left over from a previous run

The bug is in a library rather than in your code

The answer is: The program depends on something other than its input: time, randomness, ordering, or state left over from a previous run

Two bugs are present rather than one

The answer is: The program depends on something other than its input: time, randomness, ordering, or state left over from a previous run

6.[2p]
Logging an object in a browser console logs a live reference, so expanding it later can show a state the object did not have when it was logged.

True

Correct

False

The answer is: True

7.[3p]
Which of these make a print statement more useful?

Select all that apply

Printing typeof beside the value when the type is in question

Correct

Labelling the print so the line it came from is obvious

Correct

Printing at the boundaries between functions

Correct

Printing inside every line of the failing function

The answer is: Printing `typeof` beside the value when the type is in question, Labelling the print so the line it came from is obvious, Printing at the boundaries between functions

8.[3p]
Where should an assertion be placed while hunting a bug?

On the invariant that would have to break for the bug to occur

Correct

On the final result, to confirm the symptom

The answer is: On the invariant that would have to break for the bug to occur

At the top of every function in the file

The answer is: On the invariant that would have to break for the bug to occur

Only in code that is about to be released

The answer is: On the invariant that would have to break for the bug to occur

9.[2p]
Before `git bisect` can be trusted, one thing must exist: a single command that answers good or bad reliably. What is that called, in one word?

CorrectNot quite: reproduction

1.[3p] Put the steps of the debugging method in order.

2.[3p] A bug lies somewhere in a 1000 line region. How many checks does binary search need, at most, to reach a single line?

3.[2p] A test passed at a release 512 commits ago and fails now. How many builds does git bisect need in the worst case?

4.[3p] Why is "something is wrong with the sorting" a useless hypothesis?

5.[3p] A bug appears only sometimes, on the same input. What does intermittency usually mean?

6.[2p] Logging an object in a browser console logs a live reference, so expanding it later can show a state the object did not have when it was logged.

7.[3p] Which of these make a print statement more useful?

8.[3p] Where should an assertion be placed while hunting a bug?

9.[2p] Before git bisect can be trusted, one thing must exist: a single command that answers good or bad reliably. What is that called, in one word?

1.[3p]
Put the steps of the debugging method in order.

2.[3p]
A bug lies somewhere in a 1000 line region. How many checks does binary search need, at most, to reach a single line?

3.[2p]
A test passed at a release 512 commits ago and fails now. How many builds does `git bisect` need in the worst case?

4.[3p]
Why is "something is wrong with the sorting" a useless hypothesis?

5.[3p]
A bug appears only sometimes, on the same input. What does intermittency usually mean?

6.[2p]
Logging an object in a browser console logs a live reference, so expanding it later can show a state the object did not have when it was logged.

7.[3p]
Which of these make a print statement more useful?

8.[3p]
Where should an assertion be placed while hunting a bug?

9.[2p]
Before `git bisect` can be trusted, one thing must exist: a single command that answers good or bad reliably. What is that called, in one word?