diff --git a/swh/loader/mercurial/tests/data/build.py b/swh/loader/mercurial/tests/data/build.py
new file mode 100755
index 0000000..7ef0ca1
--- /dev/null
+++ b/swh/loader/mercurial/tests/data/build.py
@@ -0,0 +1,265 @@
+#!/usr/bin/env python
+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+"""
+This build script purpose is to create example repositories from bash scripts
+and extract assertion data from them into json files.
+
+Advantages:
+
+    - the bash script documents the repository creation
+    - automating creation allow easy repository update
+    - automation extraction allow easier update of assertion data
+
+Create a new repository
+-----------------------
+
+First, create a bash script `myscript.sh` which will serve to create, update
+and document the repository.
+
+Here is a minimal working example:
+
+    #!/usr/bin/env bash
+
+    # Setup bash in strict mode
+    set -euo pipefail
+
+    # Allow direct call to call the script: `./myscript.sh repository-name`
+    if [ ! -z "$1" ]; then
+        HG_REPO="$1"
+    fi
+
+    # Prepare the repository
+    hg init "$HG_REPO"
+    cd "$HG_REPO"
+    cat > .hg/hgrc << EOL
+        [ui]
+        username = Full Name<full.name@domain.tld>
+    EOL
+
+    # Populate the repository
+    touch README.md
+    hg add README.md
+    hg commit -m "Add README"
+
+Then build the repository and the associated json file which containing
+the repository objects identities:
+
+    ./build.py json myscript.sh
+
+You should now have a `myscript.tgz` containing the repository
+and a `myscript.json` with the repository objects identities.
+
+Update a repository
+-------------------
+
+When there is a build script file:
+
+    Update the source `repository.sh` and run `./build.py json repository.sh`.
+    New `tgz` and `json` files will be produced.
+    The old files will be renamed.
+
+When There is no build script file:
+
+    Maybe consider not updating the repository and add a new one instead.
+
+    Otherwise, uncompress the `repository.tgz`, manually update the `repository`
+    and run `./build.py json repository`.
+    New `tgz` and `json` files will be produced.
+    The old files will be renamed.
+
+Extract json from existing repository
+-------------------------------------
+
+For existing repository without build scripts it is possible to extract
+the corresponding json file by running `./build.py json repository.tgz`
+"""
+
+import json
+import shutil
+import subprocess
+from datetime import datetime
+from pathlib import Path
+
+import click
+
+
+def abort(message):
+    """Abort the script with a message."""
+    click.echo(message, err=True)
+    click.get_current_context().abort()
+
+
+def backup(path: Path):
+    """Rename an existing path."""
+    click.echo(f"Creating backup of {path}")
+    now = datetime.now()
+    backup_path = path.with_suffix(f"{path.suffix}.bak.{now:%Y%m%d%H%M%S}")
+    path.rename(backup_path)
+    click.echo(f"Backup created: {str(backup_path)!r}")
+
+
+def _build_repository(script: str) -> Path:
+    """Build a repository from a bash script."""
+    script_path = Path(script).absolute()
+
+    if not script_path.exists():
+        abort(f"Path {script_path!r} does not exists.")
+
+    if script_path.suffix != ".sh":
+        abort(f"Wrong suffix: {script_path.suffix!r}. Expected: '.sh'")
+
+    repository_path = script_path.with_suffix("")
+
+    if repository_path.exists():
+        backup(repository_path)
+
+    click.echo(f"Running build script: {str(script_path)!r}")
+    subprocess.call(
+        ["bash", "-euo", "pipefail", script_path], env={"HG_REPO": str(repository_path)}
+    )
+
+    return repository_path
+
+
+def _build_json(source: str) -> Path:
+    if source.endswith(".tgz"):
+        archive_path = Path(source).absolute()
+        repository_path = archive_path.with_suffix("")
+
+        if repository_path.exists():
+            backup(repository_path)
+
+        subprocess.call(["tar", "-xf", archive_path], cwd=archive_path.parent)
+    elif source.endswith(".sh"):
+        repository_path = _build_repository(source)
+    else:
+        repository_path = Path(source).absolute()
+
+    click.echo(f"Extracting object identities: {str(repository_path)!r}")
+    output = subprocess.check_output(["swh-hg-identify", "all"], cwd=repository_path)
+    lines = output.decode().splitlines()
+
+    directory_swhids = []
+    revision_swhids = []
+    release_swhids = []
+
+    for line in lines:
+        uri, _ = line.split("\t")
+        _, _, swhid_type, swhid = uri.split(":")
+        if swhid_type == "dir":
+            directory_swhids.append(swhid)
+        elif swhid_type == "rev":
+            revision_swhids.append(swhid)
+        elif swhid_type == "rel":
+            release_swhids.append(swhid)
+        elif swhid_type == "snp":
+            snapshot_swhid = swhid
+        else:
+            abort(f"{line!r} unknown type {swhid_type!r}")
+
+    json_path = repository_path.with_suffix(".json")
+
+    if json_path.exists():
+        backup(json_path)
+
+    click.echo(f"Creating object identities file: {str(json_path)!r}")
+    json_path.write_text(
+        json.dumps(
+            {
+                "directories": directory_swhids,
+                "revisions": revision_swhids,
+                "releases": release_swhids,
+                "snapshot": snapshot_swhid,
+            }
+        )
+    )
+
+    return json_path
+
+
+@click.group(help=__doc__.split("\n\n")[0])
+def main():
+    pass
+
+
+@main.command()
+def man():
+    """Display script's manual."""
+    click.echo(__doc__)
+
+
+@main.command("repository")
+@click.argument("script")
+def build_repository(script: str):
+    """Build a repository.
+
+    SCRIPT must be is a bash script with a `.sh` suffix
+
+    The generated repository will have the same path minor the `.sh` suffix.
+
+    The script will be passed repository name as the `HG_REPO` environment variable.
+    """
+    _build_repository(script)
+
+
+@main.command("json")
+@click.argument("source")
+def build_json(source: str):
+    """Build a json file of object identities.
+
+    SOURCE can be a script as required by the `repository` command
+    (see repository --help), a repository archive, or an existing repository.
+
+    The produced file will have the source path with the `.json` suffix.
+    """
+    _build_json(source)
+
+
+@main.command("archive")
+@click.option(
+    "--clean", "-c", default=False, is_flag=True, help="Remove created artifacts",
+)
+@click.argument("source")
+def build_archive(source: str, clean: bool = False):
+    """Build a repository archive and is associated json file.
+
+    SOURCE can be a script as required by the `repository` command
+    (see repository --help), or an existing repository.
+
+    The produced archive will have the source path with the `.tgz` suffix.
+    The produced json file will have the source path with the `.json` suffix.
+    """
+    if source.endswith(".sh"):
+        repository_path = _build_repository(source)
+    else:
+        repository_path = Path(source).absolute()
+        if not (repository_path / ".hg").exists():
+            abort(f"{str(repository_path)!r} is not a Mercurial repository")
+
+    json_path = _build_json(str(repository_path))
+
+    archive_path = repository_path.with_suffix(".tgz")
+    if archive_path.exists():
+        backup(archive_path)
+
+    subprocess.call(
+        [
+            "tar",
+            "-cf",
+            archive_path.relative_to(archive_path.parent),
+            repository_path.relative_to(archive_path.parent),
+            json_path.relative_to(archive_path.parent),
+        ],
+        cwd=archive_path.parent,
+    )
+
+    if clean:
+        shutil.rmtree(repository_path)
+        json_path.unlink()
+
+
+if __name__ == "__main__":
+    main()