tmp_path and tmp_path_factory in PyTest - Build an Automation Script

Create and verify temporary files using tmp_path and tmp_path_factory in pytest

Preconditions (2)

Step 1: Use the tmp_path fixture to create a temporary directory

Step 2: Inside this directory, create a file named 'testfile.txt' with content 'Hello pytest!'

Step 3: Verify that the file exists and contains the correct content

Step 4: Use the tmp_path_factory fixture to create a new temporary directory with a custom prefix 'myprefix'

Step 5: Inside this new directory, create a file named 'factoryfile.txt' with content 'Factory test content'

Step 6: Verify that this file exists and contains the correct content

✅ Expected Result: Both files are created successfully in their respective temporary directories with the correct content, and the directories are unique and cleaned up after tests

Automation Requirements - pytest

Assertions Needed:

Assert that 'testfile.txt' exists in tmp_path directory

Assert that the content of 'testfile.txt' is 'Hello pytest!'

Assert that 'factoryfile.txt' exists in the directory created by tmp_path_factory

Assert that the content of 'factoryfile.txt' is 'Factory test content'

Best Practices:

Use pytest fixtures tmp_path and tmp_path_factory for isolated temporary directories

Use pathlib.Path methods for file operations

Use assertions to verify file existence and content

Avoid hardcoding absolute paths

Let pytest handle cleanup of temporary directories

Automated Solution

PyTest

import pytest


def test_tmp_path_and_tmp_path_factory(tmp_path, tmp_path_factory):
    # Using tmp_path fixture
    test_file = tmp_path / "testfile.txt"
    test_file.write_text("Hello pytest!")
    
    # Assert file exists
    assert test_file.exists(), f"File {test_file} should exist"
    
    # Assert file content
    content = test_file.read_text()
    assert content == "Hello pytest!", f"File content should be 'Hello pytest!' but got '{content}'"

    # Using tmp_path_factory fixture
    custom_dir = tmp_path_factory.mktemp("myprefix")
    factory_file = custom_dir / "factoryfile.txt"
    factory_file.write_text("Factory test content")

    # Assert file exists
    assert factory_file.exists(), f"File {factory_file} should exist"

    # Assert file content
    factory_content = factory_file.read_text()
    assert factory_content == "Factory test content", f"File content should be 'Factory test content' but got '{factory_content}'"

This test function uses two pytest fixtures: tmp_path and tmp_path_factory.

First, tmp_path provides a temporary directory unique to this test. We create a file testfile.txt inside it and write text. We then check if the file exists and if its content matches what we wrote.

Next, tmp_path_factory is used to create another temporary directory with a custom prefix myprefix. Inside this directory, we create another file factoryfile.txt and write different content. We verify the file's existence and content similarly.

Using pathlib's Path methods makes file handling easy and readable. Assertions ensure the test fails if files are missing or contents are wrong. Pytest automatically cleans up these temporary directories after the test finishes, so no manual cleanup is needed.

Common Mistakes - 4 Pitfalls

Using string paths instead of pathlib.Path objects for file operations

Not asserting file existence before reading content

Hardcoding absolute paths or assuming fixed directory locations

{'mistake': 'Manually deleting temporary files or directories', 'why_bad': 'Pytest automatically cleans up temporary directories; manual deletion can cause errors or race conditions.', 'correct_approach': "Rely on pytest's automatic cleanup and avoid manual file or directory removal."}

Bonus Challenge

Now add data-driven testing to create multiple files with different names and contents using tmp_path

Show Hint

Practice

1. What is the main purpose of the tmp_path fixture in pytest?

easy

A. To provide a unique temporary directory for each test function

B. To create multiple temporary directories during a single test

C. To permanently store test files after tests finish

D. To mock file system calls without creating real files

Solution

1. Step 1: Understand the role of tmp_path

   The tmp_path fixture gives each test a fresh temporary directory to use.

2. Step 2: Compare with other options

   It does not create multiple directories per test (that's tmp_path_factory), nor does it store files permanently or mock file calls.

3. Final Answer:

   To provide a unique temporary directory for each test function -> Option A

4. Quick Check:

   tmp_path = unique temp folder per test [OK]

Hint: Remember: tmp_path = one temp folder per test [OK]

Common Mistakes:

• Confusing tmp_path with tmp_path_factory
• Thinking tmp_path stores files permanently
• Assuming tmp_path mocks file system calls

2. Which of the following is the correct way to use tmp_path_factory to create a new temporary directory named 'data' inside a test?

easy

A. new_dir = tmp_path_factory.make_directory('data')

B. new_dir = tmp_path_factory.create_temp('data')

C. new_dir = tmp_path_factory.tempdir('data')

D. new_dir = tmp_path_factory.mktemp('data')

Solution

1. Step 1: Recall the correct method name

   The method to create a new temporary directory with tmp_path_factory is mktemp().

2. Step 2: Verify method usage

   Calling tmp_path_factory.mktemp('data') creates a temp directory named 'data'. Other options are not valid pytest methods.

3. Final Answer:

   new_dir = tmp_path_factory.mktemp('data') -> Option D

4. Quick Check:

   mktemp() creates temp dirs [OK]

Hint: Use mktemp() method to create temp dirs with tmp_path_factory [OK]

Common Mistakes:

• Using incorrect method names like create_temp or tempdir
• Trying to call make_directory which doesn't exist
• Confusing tmp_path and tmp_path_factory usage

3. Given the following pytest test code, what will be the output of the assertion?

def test_create_file(tmp_path):
    file = tmp_path / 'test.txt'
    file.write_text('hello')
    content = file.read_text()
    assert content == 'hello'

medium

A. Test fails because read_text() returns bytes, not string

B. Test fails because the file is not created

C. Test passes because the file content matches 'hello'

D. Test raises an exception due to invalid file path

Solution

1. Step 1: Analyze file creation and writing

   The code creates a file 'test.txt' in the temporary directory and writes the string 'hello' to it.

2. Step 2: Check reading and assertion

   Reading the file with read_text() returns the string 'hello', which matches the assertion.

3. Final Answer:

   Test passes because the file content matches 'hello' -> Option C

4. Quick Check:

   write_text/read_text with tmp_path works [OK]

Hint: write_text and read_text handle strings correctly [OK]

Common Mistakes:

• Assuming read_text returns bytes instead of string
• Thinking file is not created automatically
• Expecting exceptions from valid path operations

4. Identify the error in this pytest test using tmp_path_factory:

def test_dir_creation(tmp_path_factory):
    dir1 = tmp_path_factory.mktemp('dir')
    dir2 = tmp_path_factory.mktemp('dir')
    assert dir1 != dir2

medium

A. Error because mktemp cannot create directories with the same name

B. No error; test passes because mktemp creates unique dirs

C. Error because tmp_path_factory is not a valid fixture

D. Error because assert compares directory contents, not paths

Solution

1. Step 1: Understand mktemp behavior

   Each call to mktemp('dir') creates a unique temporary directory, even if the name is the same.

2. Step 2: Check assertion validity

   The assertion compares the two directory paths and expects them to be different, which is true.

3. Final Answer:

   No error; test passes because mktemp creates unique dirs -> Option B

4. Quick Check:

   mktemp creates unique dirs even with same name [OK]

Hint: mktemp always creates unique dirs, names can repeat [OK]

Common Mistakes:

• Thinking mktemp fails on duplicate names
• Confusing fixture names or usage
• Assuming assert compares contents, not paths

5. You want to write a pytest test that creates two temporary directories: one shared across multiple tests and one unique per test. Which combination of fixtures should you use?

hard

A. Use tmp_path_factory to create the shared directory and tmp_path for the unique per-test directory

B. Use tmp_path for both shared and unique directories

C. Use tmp_path_factory for both shared and unique directories

D. Use tmp_path to create the shared directory and tmp_path_factory for unique directories

Solution

1. Step 1: Identify fixture roles

   tmp_path provides a fresh temp directory unique to each test. tmp_path_factory can create directories shared or reused across tests.

2. Step 2: Match requirements to fixtures

   For a shared directory across tests, use tmp_path_factory. For unique per-test directories, use tmp_path.

3. Final Answer:

   Use tmp_path_factory to create the shared directory and tmp_path for the unique per-test directory -> Option A

4. Quick Check:

   tmp_path unique per test, tmp_path_factory for shared [OK]

Hint: tmp_path unique per test; tmp_path_factory for shared dirs [OK]

Common Mistakes:

• Using tmp_path for shared directories
• Using tmp_path_factory only for unique per-test dirs
• Mixing up fixture purposes