docs(fixtures): add instructions for adding new fixtures

.github/fixtures/README.md

@@ -0,0 +1,28 @@
+# Fixtures
+
+[Test fixtures](https://en.wikipedia.org/wiki/Test_fixture) are a way of testing the `git-cliff`'s functionality against a configuration file (`cliff.toml`) and asserting the output (`expected.md`).
+
+They are being [run](https://github.com/orhun/git-cliff/actions/workflows/test-fixtures.yml) as a part of the GitHub Actions and the workflow file can be viewed [here](../workflows/test-fixtures.yml).
+
+## Adding new fixtures
+
+1. Copy the `new-fixture-template` as `test-<functionality>`.
+2. Update the files accordingly to the function that is being tested.
+3. Run the fixture locally. (see below)
+4. Add the fixture to [`test-fixtures.yml`](../workflows/test-fixtures.yml) matrix.
+   - If you need to specify custom arguments to `git-cliff` for the fixture test, you can do it here with using `command`.
+5. Commit your changes.
+
+See [this commit](https://github.com/orhun/git-cliff/commit/c94cb6a37ae268953ab29dd35cb43b6a4fec47cc) as an example.
+
+## Running locally
+
+To run the fixtures locally:
+
+```sh
+./test-fixtures-locally.sh <fixture_name>
+```
+
+## See also
+
+- [Contribution Guidelines](https://github.com/orhun/git-cliff/blob/main/CONTRIBUTING.md)

.github/fixtures/new-fixture-template/cliff.toml

@@ -0,0 +1,37 @@
+[changelog]
+# changelog header
+header = """
+# Changelog\n
+All notable changes to this project will be documented in this file.\n
+"""
+# template for the changelog body
+# https://keats.github.io/tera/docs/#introduction
+body = """
+{% if version %}\
+    ## [{{ version | trim_start_matches(pat="v") }}] - {{ timestamp | date(format="%Y-%m-%d") }}
+{% else %}\
+    ## [unreleased]
+{% endif %}\
+{% for group, commits in commits | group_by(attribute="group") %}
+    ### {{ group | upper_first }}
+    {% for group, commits in commits | group_by(attribute="scope") %}
+        #### {{ group | upper_first }}
+        {% for commit in commits %}
+            - {{ commit.message | upper_first }}\
+        {% endfor %}
+    {% endfor %}\
+{% endfor %}\n
+"""
+# template for the changelog footer
+footer = """
+<!-- generated by git-cliff -->
+"""
+# remove the leading and trailing whitespace from the templates
+trim = true
+
+[git]
+# regex for parsing and grouping commits
+commit_parsers = [
+    { message = "^feat", group = "Features", default_scope = "app" },
+    { message = "^fix", group = "Bug Fixes", scope = "cli" },
+]

.github/fixtures/new-fixture-template/commit.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+set -e
+
+GIT_COMMITTER_DATE="2022-04-06 01:25:08" git commit --allow-empty -m "Initial commit"
+GIT_COMMITTER_DATE="2022-04-06 01:25:09" git commit --allow-empty -m "feat: add feature 1"
+GIT_COMMITTER_DATE="2022-04-06 01:25:10" git commit --allow-empty -m "fix: fix feature 1"
+git tag v0.1.0
+GIT_COMMITTER_DATE="2022-04-06 01:25:11" git commit --allow-empty -m "feat(gui): add feature 2"
+GIT_COMMITTER_DATE="2022-04-06 01:25:12" git commit --allow-empty -m "fix(gui): fix feature 2"
+git tag v0.2.0
+GIT_COMMITTER_DATE="2022-04-06 01:25:13" git commit --allow-empty -m "test: add tests"

.github/fixtures/new-fixture-template/expected.md

@@ -0,0 +1,37 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+## [unreleased]
+
+### Test
+
+## [0.2.0] - 2022-04-05
+
+### Bug Fixes
+
+#### Cli
+
+- Fix feature 2
+
+### Features
+
+#### Gui
+
+- Add feature 2
+
+## [0.1.0] - 2022-04-05
+
+### Bug Fixes
+
+#### Cli
+
+- Fix feature 1
+
+### Features
+
+#### App
+
+- Add feature 1
+
+<!-- generated by git-cliff -->

.github/workflows/test-fixtures.yml

@@ -16,6 +16,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - fixtures-name: new-fixture-template
           - fixtures-name: test-ignore-tags
           - fixtures-name: test-topo-order
             command: --latest