mutmut

https://mutmut.readthedocs.io/en/latest
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Mutmut is a Python mutation testing system focused on ease of use, featuring incremental work,...
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### Install and run mutmut

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Basic commands to install the package and initiate a mutation testing run.

```bash
pip install mutmut
mutmut run
```

--------------------------------

### Skip mutation for a code region

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Use start and end markers to suppress mutation across a range of lines regardless of indentation.

```python
a = mutate_this()

# pragma: no mutate start
b = skip_this()
c = skip_this_too()
# pragma: no mutate end

d = mutate_this_too()
```

--------------------------------

### Configure mutmut in setup.cfg

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Define source paths and test selection arguments in the project's setup.cfg file.

```ini
[mutmut]
source_paths=src/
pytest_add_cli_args_test_selection=tests/
```

--------------------------------

### Configure additional files to copy

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Specify extra directories or files required for the test suite to run correctly.

```ini
also_copy=
    iommi/snapshots/
    conftest.py
```

--------------------------------

### Configure mutmut in pyproject.toml

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Define source paths and test selection arguments using the tool.mutmut section in pyproject.toml.

```toml
[tool.mutmut]
source_paths = [ "src/" ]
pytest_add_cli_args_test_selection= [ "tests/" ]
```

--------------------------------

### Run mutmut with wildcard patterns

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Use Unix-style filename patterns to target specific modules or functions for mutation testing.

```bash
mutmut run "my_module*"
mutmut run "my_module.my_function*"
```

--------------------------------

### Configure mutation timeout settings

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Adjust the timeout calculation parameters for slow mutations.

```python
# Configure how long mutmut waits before killing a slow mutation
# Currently calculated as (duration_of_original_tests + timeout_constant) * timeout_multiplier seconds
timeout_constant = 1.0
timeout_multiplier = 15.0
```

--------------------------------

### Enable debug output

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Increase verbosity to display detailed test output for debugging purposes.

```ini
debug=true
```

--------------------------------

### Set dependency change behavior

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Control the action taken when a watched dependency file changes.

```python
on_dependency_change = "warn"
```

--------------------------------

### Configure type checker filtering

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Set the command used to run type checkers like mypy or pyrefly to filter out invalid mutants.

```ini
# for pyrefly
type_check_command = ['pyrefly', 'check', '--output-format=json']
# for mypy
type_check_command = ['mypy', 'your_source_dir', '--output', 'json', '--disable-error-code', 'unused-ignore']
```

--------------------------------

### Enable coverage-based line filtering

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Restrict mutation to only those lines identified as covered by coverage.py.

```ini
mutate_only_covered_lines=true
```

--------------------------------

### Configure cache invalidation files

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Specify additional files to watch for changes using glob patterns to trigger cache invalidation.

```python
cache_invalidation_files = [ "queries/*.sql", "config/*.yaml" ]
```

--------------------------------

### Exclude files from mutation

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Define specific files or patterns to include or exclude from the mutation process.

```ini
only_mutate=
    src/api/*
    src/services/*
do_not_mutate=
    *__tests.py
```

--------------------------------

### Skip mutation for functions or classes

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Place the pragma inline on the definition line to exclude the entire node and its children from mutation.

```python
def complex_algorithm():  # pragma: no mutate block
    return some_complex_calculation()

class MySettings:  # pragma: no mutate block
    DEBUG = True
    MAX_RETRIES = 3
```

--------------------------------

### Skip mutation for a single line

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Append the pragma comment to a specific line to prevent it from being mutated.

```python
some_code_here()  # pragma: no mutate
```

--------------------------------

### Disable git change detection

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Force mutmut to use the curated-list fallback instead of git-based change detection.

```python
use_git_change_detection = false
```

--------------------------------

### Exclude files from cache invalidation

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Define glob patterns for files that should be ignored during dependency change detection.

```python
cache_invalidation_exclude = [ "*.json", "fixtures/snapshots/*" ]
```

--------------------------------

### Disable setproctitle in pyproject.toml

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Override the default setproctitle behavior by setting the use_setproctitle option in the tool.mutmut configuration section.

```toml
# pyproject.toml
[tool.mutmut]
use_setproctitle = false
```

--------------------------------

### Exclude code patterns via regex

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Define patterns in pyproject.toml to prevent mutmut from mutating specific expressions matching the provided regex.

```toml
# pyproject.toml
[tool.mutmut]
do_not_mutate_patterns = [
    # disable mutations of all logger.info/debug/... statements
    'logger\.\w+',
    # disable mutating exceptions
    'raise \w+',
]
```

--------------------------------

### Skip mutation for an if branch

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Place the pragma inline on an if statement to suppress mutation for that specific branch, leaving sibling branches mutable.

```python
if error_condition:  # pragma: no mutate block
    log_error()
    send_alert()
elif other_condition:
    # still mutated -- this branch is outside the block scope
    handle_other()
else:
    # still mutated
    handle_success()
```

--------------------------------

### Limit stack depth for relevant tests

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Restrict mutation testing relevance to tests within a specific stack depth to improve performance.

```ini
max_stack_depth=8
```

--------------------------------

### Skip mutation for a function body

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Place the pragma on its own line inside a function to suppress mutation of the body while keeping the definition mutable.

```python
def foo(val=1):
    # pragma: no mutate block
    x = 1
    y = complex_calculation()
    z = x + y

def bar():
    # this function is still mutated normally
    return 42
```

--------------------------------

### Modify pytest arguments

Source: https://mutmut.readthedocs.io/en/latest?badge=latest

Define CLI arguments for test selection or general pytest configuration overrides.

```python
# for CLI args that select or deselect tests, use `pytest_add_cli_args_test_selection`
pytest_add_cli_args_test_selection = ["-m", "not fail", "-k", "test_include"]

# for other CLI args, use `pytest_add_cli_args`
pytest_add_cli_args = ["-p", "no:some_plugin"] # disable a plugin
pytest_add_cli_args = ["-o", "xfail_strict=False"] # overrides xfail_strict from your normal config

# if you want to ignore the normal pytest configuration
# you can specify a diferent pytest ini file to be used
pytest_add_cli_args = ["-c", "mutmut_pytest.ini"]
also_copy = ["mutmut_pytest.ini"]
```
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