Comparing values (equality, inequality) in PyTest - Test Execution Trace

Test Overview

This test checks if two values are equal and if two other values are not equal using simple assertions in pytest.

Test Code - pytest

PyTest

import pytest

def test_compare_values():
    a = 5
    b = 5
    c = 10
    d = 20

    assert a == b, "Values a and b should be equal"
    assert c != d, "Values c and d should not be equal"

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	—	PASS
2	Assign values a=5, b=5, c=10, d=20	Variables set in test function	—	PASS
3	Assert that a equals b	a=5, b=5	Check if a == b	PASS
4	Assert that c does not equal d	c=10, d=20	Check if c != d	PASS
5	Test ends successfully	All assertions passed	—	PASS

Failure Scenario

Failing Condition: If a and b are not equal or c and d are equal

Execution Trace Quiz - 3 Questions

What does the assertion 'assert a == b' check?

A If a is less than b

B If a and b have the same value

C If a is greater than b

D If a and b are different types

Key Result

Use clear and simple assertions to compare values. Always include a helpful message in assertions to understand failures quickly.

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