Fondant build - add test case and documentation (#546)

This PR adds documentation and a test case for the fondant build
command.

fix #530

docs/components/custom_component.md

@@ -21,7 +21,8 @@ To implement a custom component, a couple of files need to be defined:
 
 Each Fondant component is defined by a specification which describes its interface. This
 specification is represented by a single `fondant_component.yaml` file. See the [component
-specification page](../components/component_spec.md) for info on how to write the specification for your component.
+specification page](../components/component_spec.md) for info on how to write the specification for
+your component.
 
 ## Main.py script
 
@@ -64,8 +65,8 @@ class ExampleComponent(PandasTransformComponent):
 ```
 
 The `__init__` method is called once for each component class with custom arguments defined in the
-`args` section of the [component specification](../components/component_spec.md).) This is a good 
-place to initialize resources and costly initializations such as network connections, models, 
+`args` section of the [component specification](../components/component_spec.md).) This is a good
+place to initialize resources and costly initializations such as network connections, models,
 parsing a config file, etc. By doing so, you can effectively prevent the redundant re-initialization
 of resources each time the `transform` method is invoked.
 
@@ -87,7 +88,8 @@ which is then imported in the `main.py` script.
 
 ## Dockerfile
 
-The `Dockerfile` defines how to build the component into a Docker image. An example Dockerfile is defined below.
+The `Dockerfile` defines how to build the component into a Docker image. An example Dockerfile is
+defined below.
 
 ```bash
 FROM --platform=linux/amd64 pytorch/pytorch:2.0.1-cuda11.7-cudnn8-runtime
@@ -112,11 +114,39 @@ ENTRYPOINT ["fondant", "execute", "main"]
 
 ## Requirements.txt
 
-A `requirements.txt` file lists the Python dependencies of the component. Note that any Fondant component will always have `Fondant` as the minimum requirement. It's important to also pin the version of each dependency to make sure the component remains working as expected. Below is an example of a component that relies on several Python libraries such as Pillow, PyTorch and Transformers.
+A `requirements.txt` file lists the Python dependencies of the component. Note that any Fondant
+component will always have `Fondant` as the minimum requirement. It's important to also pin the
+version of each dependency to make sure the component remains working as expected. Below is an
+example of a component that relies on several Python libraries such as Pillow, PyTorch and
+Transformers.
 
 ```
 fondant
 Pillow==10.0.1
 torch==2.0.1
 transformers==4.29.2
 ```
+
+## Build the component
+
+Before you can use your custom component within your pipeline you have to build the component into a
+Docker container. The Fondant CLI offers a specialized `fondant build` command designed
+explicitly for this task.
+To commence the component building process, simply execute:
+
+```
+fondant build <component dir> -t <image tag>
+```
+
+Ensure that you replace `<component dir>` with the accurate path to the directory where your
+component is located. The `-t` flag is used to specify the Docker container tag.
+
+When you use the `-t` flag, the tag in the referenced component specification yaml will also be
+updated, ensuring that the next pipeline run correctly references the image.
+
+It's important to note that the `fondant build` command offers additional arguments. To access a
+complete list of all available arguments, you can execute `fondant build -h`.
+
+
+
+

tests/example_component/Dockerfile

@@ -0,0 +1 @@
+FROM --platform=linux/amd64 python:3.8-slim as base

tests/example_component/fondant_component.yaml

@@ -0,0 +1,3 @@
+name: dummy component
+description: dummy component for testing purpose
+image: image:local

tests/test_cli.py

@@ -1,11 +1,13 @@
 import argparse
 import subprocess
+from pathlib import Path
 from unittest.mock import patch
 
 import pytest
 from fondant.cli import (
     ComponentImportError,
     PipelineImportError,
+    build,
     compile_kfp,
     compile_local,
     compile_vertex,
@@ -314,3 +316,51 @@ def test_vertex_run(tmp_path_factory):
             service_account=None,
             network=None,
         )
+
+
+@patch("docker.api.client.APIClient.push")
+@patch("docker.api.client.APIClient.build")
+def test_component_build(mock_build, mock_push):
+    """Test that the build command works as expected."""
+    args = argparse.Namespace(
+        component_dir=Path(__file__).parent / "example_component",
+        tag="image:test",
+        build_arg=["key=value"],
+        nocache=True,
+        pull=True,
+        target="base",
+    )
+
+    # Set up the return values for the mocked methods
+    mock_build.return_value = ["Dummy logs build"]
+    mock_push.return_value = [{"status": "dummy log status"}]
+
+    # Run build command
+    build(args)
+
+    # Check that docker build and push were executed correctly
+    mock_build.assert_called_with(
+        path=str(Path(__file__).parent / "example_component"),
+        tag="image:test",
+        buildargs={"key": "value"},
+        nocache=True,
+        pull=True,
+        target="base",
+        decode=True,
+    )
+
+    mock_push.assert_called_with("image", tag="test", stream=True, decode=True)
+
+    # Check that the component specification file was updated correctly
+    with open(
+        Path(__file__).parent / "example_component" / "fondant_component.yaml",
+        "r+",
+    ) as f:
+        content = f.read()
+        assert "image:test" in content
+
+        # Revert image name in component specification
+        content = content.replace("image:test", "image:local")
+        f.seek(0)
+        f.write(content)
+        f.truncate()