### Install pytest-regressions via pip

Source: https://pytest-regressions.readthedocs.io/en/latest/installation.html

Standard installation command for the base package.

```bash
$ pip install pytest-regressions
```

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

### Install pytest-regressions via conda

Source: https://pytest-regressions.readthedocs.io/en/latest/installation.html

Installation command for users of the conda package manager.

```bash
$ conda install -c conda-forge pytest-regressions
```

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

### Install pytest-regressions with extra dependencies

Source: https://pytest-regressions.readthedocs.io/en/latest/installation.html

Install the package with support for dataframe, num, or image fixtures.

```bash
$ pip install pytest-regressions[dataframe,num,image]
```

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

### Example failure message

Source: https://pytest-regressions.readthedocs.io/en/latest/overview.html

The output displayed when a regression file is missing and needs to be created.

```text
>           pytest.fail(msg)
E           Failed: File not found in data directory, created:
E           - C:\Users\bruno\pytest-regressions\tests\test_grids\test_grids2.yml
```

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

### Manual assertion test

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

An example of manual assertions that are prone to maintenance issues as data grows.

```python
def test_grids():
    data = summary_grids()
    assert data["Main Grid"]["id"] == 0
    assert data["Main Grid"]["cell_count"] == 1000
    assert data["Main Grid"]["active_cells"] == 300
    assert data["Main Grid"]["properties"] == [
        {"name": "Temperature", "min": 75, "max": 85},
        {"name": "Porosity", "min": 0.3, "max": 0.4},
    ]
    ...
```

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

### Define a sample data function

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

A function returning a dictionary representing simulation grid data for testing purposes.

```python
def summary_grids():
    return {
        "Main Grid": {
            "id": 0,
            "cell_count": 1000,
            "active_cells": 300,
            "properties": [
                {"name": "Temperature", "min": 75, "max": 85},
                {"name": "Porosity", "min": 0.3, "max": 0.4},
            ],
        },
        "Refin1": {
            "id": 1,
            "cell_count": 48,
            "active_cells": 44,
            "properties": [
                {"name": "Temperature", "min": 78, "max": 81},
                {"name": "Porosity", "min": 0.36, "max": 0.39},
            ],
        },
    }
```

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

### Generate dynamic filenames with request fixture

Source: https://pytest-regressions.readthedocs.io/en/latest/overview.html

Combine the request fixture with basename to create filenames based on the test name with custom prefixes or suffixes.

```python
def test_grids3(data_regression, data1, data2, request):
    data_regression.check(data1, basename=f"{request.node.name}_data1")
    data_regression.check(data2, basename=f"{request.node.name}_data2")
```

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

### Use data_regression fixture

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

Simplifies testing by using the data_regression fixture to automatically check dictionary data against a baseline file.

```python
def test_grids2(data_regression):
    data = summary_grids()
    data_regression.check(data)
```

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

### Register custom ini options

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

Registers custom configuration options in conftest.py to support directory overrides.

```python
def pytest_addoption(parser):
    parser.addini("lazy_datadir", "my own datadir for pytest-regressions")
    parser.addini("original_datadir", "my own original_datadir for pytest-regressions")
```

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

### Regenerate all regression files

Source: https://pytest-regressions.readthedocs.io/en/latest/overview.html

Use the --regen-all flag to update all regression files without failing the tests.

```bash
$ pytest --regen-all
```

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

### Override data directory paths

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

Configures custom data directories by overriding the lazy_datadir and original_datadir fixtures.

```python
import pytest
from pathlib import Path
from myapp.config import PATH


@pytest.fixture(scope="session")
def lazy_datadir() -> Path:
    return PATH.repo / "test-data-regression"


@pytest.fixture(scope="session")
def original_datadir() -> Path:
    return PATH.repo / "test-data-regression"
```

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

### Generated YAML baseline file

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

The format of the baseline file generated by the data_regression fixture.

```yaml
Main Grid:
  active_cells: 300
  cell_count: 1000
  id: 0
  properties:
  - max: 85
    min: 75
    name: Temperature
  - max: 0.4
    min: 0.3
    name: Porosity
Refin1:
  active_cells: 44
  cell_count: 48
  id: 1
  properties:
  - max: 81
    min: 78
    name: Temperature
  - max: 0.39
    min: 0.36
    name: Porosity
```

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

### DataRegressionFixture.check

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/api.rst.txt

Checks data against a reference file.

```APIDOC
## DataRegressionFixture.check

### Description
Verifies that the provided data matches the stored reference data.
```

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

### Force regeneration of regression files

Source: https://pytest-regressions.readthedocs.io/en/latest/overview.html

Use the --force-regen flag to update expected regression files when implementation changes are intentional.

```bash
$ pytest --force-regen
```

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

### Configure data directories via ini file

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

Defines custom data directory paths in the pytest configuration file.

```ini
[pytest]
lazy_datadir = mydatadir
original_datadir = my_originaldatadir
```

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

### ImageRegressionFixture.check

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/api.rst.txt

Checks image data against a reference file.

```APIDOC
## ImageRegressionFixture.check

### Description
Verifies that the provided image data matches the stored reference image.
```

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

### FileRegressionFixture.check

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/api.rst.txt

Checks file content against a reference file.

```APIDOC
## FileRegressionFixture.check

### Description
Verifies that the content of a file matches the stored reference file.
```

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

### Check numeric data with num_regression

Source: https://pytest-regressions.readthedocs.io/en/latest/api.html

Verifies a dictionary of numeric arrays against a recorded reference file.

```python
num_regression.check({
    'U_gas': U[0][positions],
    'U_liquid': U[1][positions],
    'gas_vol_frac [-]': vol_frac[0][positions],
    'liquid_vol_frac [-]': vol_frac[1][positions],
    'P': Pa_to_bar(P)[positions],
})
```

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

### Override fixtures using ini options

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

Implements fixture overrides that read paths from the pytest configuration.

```python
import pytest
import pathlib

@pytest.fixture(scope="session")
def original_datadir(request) -> pathlib.Path:
    config = request.config
    return config.rootpath / config.getini('original_datadir')


@pytest.fixture(scope="session")
def lazy_datadir(request) -> pathlib.Path:
    config = request.config
    return config.rootpath / config.getini('lazy_datadir')
```

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

### Parametrize tests with data_regression

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

Uses pytest parametrization to generate unique regression files for different data inputs.

```python
@pytest.mark.parametrize('data', [summary_grids(), summary_grids_2()])
def test_grids3(data_regression, data):
    data_regression.check(data)
```

```python
@pytest.mark.parametrize('data', [summary_grids(), summary_grids_2()], ids=['short', 'long'])
def test_grids3(data_regression, data):
    data_regression.check(data)
```

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

### Check NumPy ndarrays with regression fixture

Source: https://pytest-regressions.readthedocs.io/en/latest/api.html

Verifies a dictionary of NumPy arrays against recorded data using specified tolerances.

```python
def test_some_data(ndarrays_regression):
    points, values = some_function()
    ndarrays_regression.check(
        {
            'points': points,  # array with shape (100, 3)
            'values': values,  # array with shape (100,)
        },
        default_tolerance=dict(atol=1e-8, rtol=1e-8)
    )
```

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

### NumericRegressionFixture.check

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/api.rst.txt

Checks numeric data against a reference file.

```APIDOC
## NumericRegressionFixture.check

### Description
Verifies that the provided numeric data matches the stored reference data.
```

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

### NDArraysRegressionFixture.check

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/api.rst.txt

Checks numpy arrays against a reference file.

```APIDOC
## NDArraysRegressionFixture.check

### Description
Verifies that the provided numpy arrays match the stored reference data.
```

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

### Define column-specific tolerances

Source: https://pytest-regressions.readthedocs.io/en/latest/api.html

Provide a dictionary mapping DataFrame keys to specific tolerance settings for validation.

```python
tolerances={'U': dict(atol=1e-2)}
```

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

### Customize regression filenames

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/overview.rst.txt

Controls the output filename of regression data using the basename parameter.

```python
def test_grids3(data_regression, data):
    data_regression.check(data, basename="my_custom_name")
```

```python
def test_grids3(data_regression, data1, data2, request):
    data_regression.check(data1, basename=f"{request.node.name}_data1")
    data_regression.check(data2, basename=f"{request.node.name}_data2")
```

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

### Define default tolerances

Source: https://pytest-regressions.readthedocs.io/en/latest/api.html

Set global tolerance values for the check call, overriding numpy's default isclose behavior.

```python
default_tolerance=dict(atol=1e-7, rtol=1e-18).
```

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

### DataFrameRegressionFixture.check

Source: https://pytest-regressions.readthedocs.io/en/latest/_sources/api.rst.txt

Checks pandas DataFrame against a reference file.

```APIDOC
## DataFrameRegressionFixture.check

### Description
Verifies that the provided pandas DataFrame matches the stored reference data.
```

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

### Define numeric regression tolerances

Source: https://pytest-regressions.readthedocs.io/en/latest/api.html

Specifies custom absolute or relative tolerances for numeric comparisons.

```python
tolerances={'U': Tolerance(atol=1e-2)}
```

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

### Check pandas DataFrame against regression data

Source: https://pytest-regressions.readthedocs.io/en/latest/api.html

Use this method to validate a numeric pandas DataFrame against a stored reference or generate a new one.

```python
data_frame = pandas.DataFrame.from_dict({
    'U_gas': U[0][positions],
    'U_liquid': U[1][positions],
    'gas_vol_frac [-]': vol_frac[0][positions],
    'liquid_vol_frac [-]': vol_frac[1][positions],
    'P': Pa_to_bar(P)[positions],
})
dataframe_regression.check(data_frame)
```

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