Comparing values (equality, inequality) in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the assertion assert a == b check in pytest?

It checks if the value of a is equal to the value of b. If they are equal, the test passes; if not, it fails.

beginner

How do you assert that two values are not equal in pytest?

Use assert a != b to check that a and b are different. The test passes if they are not equal.

intermediate

Why is it better to use assert a == b instead of if a != b: raise AssertionError in pytest?

Because assert statements are simpler, clearer, and pytest shows detailed error messages automatically when assertions fail.

beginner

What happens if an equality assertion fails in pytest?

The test stops and pytest reports a failure showing the values of both sides to help you understand why they differ.

intermediate

Can you compare complex data types like lists or dictionaries using equality assertions in pytest?

Yes, pytest can compare lists, dictionaries, and other data types using assert a == b. It checks if their contents are the same.

What does assert x != y check in pytest?

A x is not equal to y

B x is less than y

C x is greater than y

D x is equal to y

The assertion assert x != y passes only if x and y are not equal.

If assert a == b fails, what does pytest show?

A An error message showing values of a and b

B A success message

C No message

D A syntax error

Pytest shows an error message with the actual values of a and b to help debug.

Which is the best way to check equality in pytest?

A if a == b: pass else: raise Exception

B return a == b

C print(a == b)

D assert a == b

Using assert a == b is simple and integrates well with pytest reporting.

Can pytest compare two dictionaries with assert dict1 == dict2?

A No, it only compares numbers

B Only if they have the same keys

C Yes, it compares their contents

D Only if they are the same object

Pytest compares dictionaries by checking if all keys and values match.

What does assert a != b do if a and b are equal?

A Passes the test

B Fails the test

C Raises a syntax error

D Ignores the assertion

The assertion fails because it expects a and b to be different.

Explain how to use pytest assertions to check if two values are equal or not equal.

Think about simple assert statements for equality and inequality.

Describe what happens when an equality assertion fails in pytest and why this is helpful.

Consider how pytest reports assertion failures.

Practice

1. Which operator in pytest assertions checks if two values are equal?

easy

A. <

B. !=

C. >

D. ==

Solution

1. Step 1: Understand equality operator

   The operator == is used to check if two values are equal in Python and pytest assertions.

2. Step 2: Differentiate from inequality

   The operator != checks if values are not equal, so it is not the correct choice for equality.

3. Final Answer:

   == -> Option D

4. Quick Check:

   Equality check = == [OK]

Hint: Use == for equality, != for inequality [OK]

Common Mistakes:

• Confusing == with !=
• Using > or < for equality
• Forgetting to use assertion keyword

2. Which of the following is the correct syntax to assert that variable a is not equal to b in pytest?

easy

A. assert a != b

B. assert a =! b

C. assert a ==! b

D. assert a = b

Solution

1. Step 1: Identify correct inequality syntax

   The correct operator for inequality is !=, so the assertion should be assert a != b.

2. Step 2: Check syntax correctness

   Options with =! or ==! are invalid syntax and will cause errors.

3. Final Answer:

   assert a != b -> Option A

4. Quick Check:

   Inequality assertion = assert a != b [OK]

Hint: Remember: inequality is !=, not =! or ==! [OK]

Common Mistakes:

• Using =! instead of !=
• Using = instead of ==
• Mixing equality and inequality operators

3. What will be the result of this pytest assertion?

def test_numbers():
    x = 10
    y = 5 + 5
    assert x == y

medium

A. Syntax error in assertion

B. Test fails because 10 does not equal 5

C. Test passes because 10 equals 10

D. Test fails because variables are different

Solution

1. Step 1: Calculate values of variables

   Variable x is 10, and y is calculated as 5 + 5, which equals 10.

2. Step 2: Evaluate assertion condition

   The assertion assert x == y checks if 10 equals 10, which is true, so the test passes.

3. Final Answer:

   Test passes because 10 equals 10 -> Option C

4. Quick Check:

   10 == 10 is True [OK]

Hint: Add values before comparing for equality [OK]

Common Mistakes:

• Assuming variables differ without calculation
• Confusing syntax errors with logic errors
• Ignoring that 5 + 5 equals 10

4. Identify the error in this pytest assertion:

def test_strings():
    s1 = "hello"
    s2 = "Hello"
    assert s1 != s2

medium

A. No error, test passes because strings differ in case

B. Syntax error due to missing parentheses

C. Assertion should use == instead of !=

D. Variables s1 and s2 are not defined

Solution

1. Step 1: Compare string values with case sensitivity

   Strings "hello" and "Hello" differ in case, so they are not equal.

2. Step 2: Check assertion correctness

   The assertion assert s1 != s2 correctly checks that the strings are not equal, so the test passes without error.

3. Final Answer:

   No error, test passes because strings differ in case -> Option A

4. Quick Check:

   "hello" != "Hello" is True [OK]

Hint: String comparison is case-sensitive by default [OK]

Common Mistakes:

• Assuming strings are equal ignoring case
• Expecting syntax error without parentheses in assert
• Confusing == and != in assertions

5. You want to write a pytest test to check that a function get_status() returns a value that is not equal to None. Which assertion is the best choice?

hard

A. assert get_status() == None

B. assert get_status() is not None

C. assert get_status() != None

D. assert get_status() is None

Solution

1. Step 1: Understand None comparison best practice

   In Python, to check if a value is not None, the recommended way is to use is not None rather than != None.

2. Step 2: Evaluate options for correctness

   assert get_status() == None checks equality to None (wrong for this case). assert get_status() != None uses != None (works but not best practice). assert get_status() is not None uses is not None which is best practice. assert get_status() is None checks if value is None (opposite of requirement).

3. Final Answer:

   assert get_status() is not None -> Option B

4. Quick Check:

   Use 'is not None' for None checks [OK]

Hint: Use 'is not None' to check for non-None values [OK]

Common Mistakes:

• Using == None instead of is None
• Using != None instead of is not None
• Confusing equality with identity for None