File system testing with tmp_path in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest tmp_path file creation

What will be the output of this pytest test when run?

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

PyTest

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

A Prints 'hello' but test fails

B Prints 'hello' and test passes

C Raises FileNotFoundError

D Prints empty string and test fails

💡 Hint

tmp_path creates a temporary directory unique to the test.

The tmp_path fixture provides a temporary directory. Writing and reading the file works as expected, so 'hello' is printed and the assertion passes.

❓ assertion

intermediate

Correct assertion for file existence with tmp_path

Which assertion correctly checks that a file named 'data.csv' exists in the tmp_path directory?

PyTest

def test_file_exists(tmp_path):
    file = tmp_path / "data.csv"
    file.write_text("id,name\n1,Alice")
    # Which assertion is correct here?

A assert file.read_text() == ''

B assert file.is_file()

C assert tmp_path.exists()

D assert file.exists()

💡 Hint

Check if the file path exists on the filesystem.

file.exists() returns True if the file exists. file.is_file() returns True only if the path points to a regular file. tmp_path.exists() checks the directory, not the file. The last option checks content, not existence.

🔧 Debug

advanced

Debug failing test with tmp_path and file write

This test fails with an error. What is the cause?

def test_write_file(tmp_path):
    file = tmp_path / "output.txt"
    file.write("data")
    assert file.read_text() == "data"

PyTest

def test_write_file(tmp_path):
    file = tmp_path / "output.txt"
    file.write("data")
    assert file.read_text() == "data"

A read_text() returns bytes, causing assertion failure

B File path is incorrect, should use str(file)

C write() is not a method on pathlib.Path, should use write_text()

D tmp_path is read-only, cannot write files

💡 Hint

Check pathlib.Path methods for writing text.

pathlib.Path objects do not have a write() method. The correct method to write text is write_text(). Using write() causes AttributeError.

🧠 Conceptual

advanced

Why use tmp_path over tmpdir in pytest?

Which reason best explains why pytest recommends using tmp_path instead of tmpdir for file system tests?

A tmp_path provides pathlib.Path objects which are more modern and easier to use

B tmpdir creates files in the system root directory causing permission errors

C tmp_path runs tests faster by caching files between tests

D tmpdir does not clean up files after tests finish

💡 Hint

Consider the type of object returned by each fixture.

tmp_path returns pathlib.Path objects which have a rich API and are preferred in modern Python. tmpdir returns py.path.local objects which are older and less standard.

❓ framework

expert

Handling cleanup of nested directories with tmp_path

In a pytest test using tmp_path, you create nested directories and files:

def test_nested(tmp_path):
    nested_dir = tmp_path / "a" / "b" / "c"
    nested_dir.mkdir(parents=True)
    file = nested_dir / "file.txt"
    file.write_text("content")
    # After test finishes, what happens to these files and directories?

A All files and directories under tmp_path are deleted automatically after the test

B Only the top-level tmp_path directory is deleted, nested files remain

C Files remain but directories are deleted, causing orphan files

D Nothing is deleted automatically; manual cleanup is required

💡 Hint

pytest tmp_path fixture manages cleanup automatically.

pytest tmp_path creates a temporary directory unique to the test and deletes it entirely after the test finishes, including all nested files and directories.

Practice

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

easy

A. To mock file system calls without creating real files

B. To permanently store test files for later use

C. To speed up test execution by caching files

D. To create a temporary directory unique to each test for safe file operations

Solution

1. Step 1: Understand tmp_path functionality

   tmp_path provides a temporary directory unique to each test run.

2. Step 2: Identify its purpose in tests

   This temporary directory allows safe creation, reading, and deletion of files without affecting the real file system.

3. Final Answer:

   To create a temporary directory unique to each test for safe file operations -> Option D

4. Quick Check:

   tmp_path = safe temp folder [OK]

Hint: Remember tmp_path is a safe temp folder for each test [OK]

Common Mistakes:

• Thinking tmp_path stores files permanently
• Confusing tmp_path with mocking file calls
• Assuming tmp_path speeds up tests by caching

2. Which of the following is the correct way to create a new file named test.txt inside the tmp_path directory in pytest?

easy

A. (tmp_path / 'test.txt').write_text('Hello')

B. tmp_path / 'test.txt'.write_text('Hello')

C. tmp_path.write_text('test.txt', 'Hello')

D. tmp_path.write('test.txt', 'Hello')

Solution

1. Step 1: Understand tmp_path usage

   tmp_path is a pathlib.Path object, so to create a file, you combine paths with / operator.

2. Step 2: Correct syntax for writing text

   Use parentheses to combine path and then call write_text() on the file path: (tmp_path / 'test.txt').write_text('Hello').

3. Final Answer:

   (tmp_path / 'test.txt').write_text('Hello') -> Option A

4. Quick Check:

   Use (tmp_path / filename).write_text() [OK]

Hint: Use parentheses to combine path before write_text() [OK]

Common Mistakes:

• Calling write_text directly on tmp_path
• Missing parentheses around path combination
• Using incorrect method names like write()

3. Given the following pytest test code using tmp_path:

def test_write_and_read(tmp_path):
    file = tmp_path / 'data.txt'
    file.write_text('pytest rocks')
    content = file.read_text()
    assert content == 'pytest rocks'

What will be the result of running this test?

medium

A. Test passes because the file content matches the assertion

B. Test fails because the file is not created

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

D. Test raises a syntax error

Solution

1. Step 1: Analyze file creation and writing

   The code creates a file named 'data.txt' in tmp_path and writes the string 'pytest rocks' correctly.

2. Step 2: Analyze reading and assertion

   Reading the file with read_text() returns the string 'pytest rocks', which matches the assertion exactly.

3. Final Answer:

   Test passes because the file content matches the assertion -> Option A

4. Quick Check:

   write_text + read_text = matching string [OK]

Hint: write_text and read_text use strings, so assertion matches [OK]

Common Mistakes:

• Thinking read_text returns bytes instead of string
• Assuming file is not created automatically
• Confusing syntax errors with runtime behavior

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

def test_file_creation(tmp_path):
    file = tmp_path / 'log.txt'
    file.write('Log entry')
    assert file.read_text() == 'Log entry'

medium

A. Missing parentheses around tmp_path / 'log.txt'

B. The assertion compares bytes to string causing failure

C. Using write() instead of write_text() causes an AttributeError

D. The test will pass without errors

Solution

1. Step 1: Check method used to write file

   Path objects do not have a write() method; the correct method to write text is write_text().

2. Step 2: Understand error caused

   Calling write() will raise an AttributeError because it does not exist on the Path object.

3. Final Answer:

   Using write() instead of write_text() causes an AttributeError -> Option C

4. Quick Check:

   Use write_text() to write strings to files [OK]

Hint: Use write_text() for writing strings to files [OK]

Common Mistakes:

• Confusing write() with write_text()
• Ignoring method errors and expecting test pass
• Assuming parentheses are missing around path

5. You want to test a function that creates multiple files inside a directory using pytest's tmp_path. Which approach correctly verifies that exactly three files named a.txt, b.txt, and c.txt exist in the temporary directory after the function runs?

hard

A. Use assert tmp_path.read_text() == 'a.txtb.txtc.txt'

B. Use assert set(f.name for f in tmp_path.iterdir()) == {'a.txt', 'b.txt', 'c.txt'}

C. Use assert tmp_path.glob('*.txt') == ['a.txt', 'b.txt', 'c.txt']

D. Use assert tmp_path.exists('a.txt') and tmp_path.exists('b.txt') and tmp_path.exists('c.txt')

Solution

1. Step 1: Understand how to list files in tmp_path

   tmp_path.iterdir() returns an iterator of Path objects for all entries in the directory.

2. Step 2: Verify file names correctly

   Extract file names with f.name and compare as a set to ensure exactly the three expected files exist.

3. Final Answer:

   Use assert set(f.name for f in tmp_path.iterdir()) == {'a.txt', 'b.txt', 'c.txt'} -> Option B

4. Quick Check:

   Use iterdir() and set comparison for exact files [OK]

Hint: Use set of filenames from iterdir() to check exact files [OK]

Common Mistakes:

• Using glob() without converting to list or set
• Trying to read tmp_path as a file
• Using exists() incorrectly on tmp_path object