diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index dd4c590..063b817 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -31,3 +31,5 @@ jobs:
         pip install --upgrade hatch
     - name: Lint
       run: hatch fmt --check
+    - name: Check types
+      run: hatch run types:check
diff --git a/.github/workflows/python-publish.yml b/.github/workflows/python-publish.yml
index 77779a2..c8cb779 100644
--- a/.github/workflows/python-publish.yml
+++ b/.github/workflows/python-publish.yml
@@ -13,7 +13,7 @@ env:
     FORCE_COLOR: "1"
 
 jobs:
-  deploy-test:
+  deploy:
 
     runs-on: ubuntu-latest
 
@@ -27,6 +27,16 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install --upgrade hatch
+    - name: Check project version
+      run: |
+        PROJECT_VERSION=$(TERM=dumb hatch version)
+
+        if [ "$PROJECT_VERSION" != "${TAG_NAME#v}" ]; then
+          echo "Wrong project version, cannot release: $PROJECT_VERSION, ${TAG_NAME#v} expected"
+          exit 1
+        fi
+      env:
+        TAG_NAME: ${{ github.ref }}
     - name: Build package
       run: hatch build
     - name: Publish package
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 14bc790..03fcc3f 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -17,6 +17,12 @@ repos:
       language: system
       pass_filenames: false
       types: [ python ]
+    - id: check-types
+      name: run mypy
+      entry: hatch run types:check
+      language: system
+      pass_filenames: false
+      types: [ python ]
     - id: format
       name: run the formatter
       entry: hatch fmt -f
diff --git a/docker-compose.yml b/docker-compose.yml
new file mode 100644
index 0000000..80778e8
--- /dev/null
+++ b/docker-compose.yml
@@ -0,0 +1,19 @@
+services:
+  kroki:
+    image: docker.io/yuzutech/kroki
+    depends_on:
+      - mermaid
+      - bpmn
+      - excalidraw
+    environment:
+      - KROKI_MERMAID_HOST=mermaid
+      - KROKI_BPMN_HOST=bpmn
+      - KROKI_EXCALIDRAW_HOST=excalidraw
+    ports:
+      - "127.0.0.1:8080:8000"
+  mermaid:
+    image: docker.io/yuzutech/kroki-mermaid
+  bpmn:
+    image: docker.io/yuzutech/kroki-bpmn
+  excalidraw:
+    image: docker.io/yuzutech/kroki-excalidraw
diff --git a/kroki/client.py b/kroki/client.py
index d0cc823..ee3893e 100644
--- a/kroki/client.py
+++ b/kroki/client.py
@@ -20,13 +20,13 @@ class DownloadedContent:
     def _ugly_temp_excalidraw_fix(self) -> None:
         """TODO: remove me, when excalidraw container works again..
         ref: https://github.com/excalidraw/excalidraw/issues/7366"""
-        self.file_content = self.file_content.replace(
+        self.file_content: bytes = self.file_content.replace(
             b"https://unpkg.com/@excalidraw/excalidraw@undefined/dist",
             b"https://unpkg.com/@excalidraw/excalidraw@0.17.1/dist",
         )
 
     def __init__(self, file_content: bytes, file_extension: str, additional_metadata: None | dict) -> None:
-        file_uuid = uuid3(NAMESPACE_OID, f"{additional_metadata}{file_content}")
+        file_uuid = uuid3(NAMESPACE_OID, f"{additional_metadata}{file_content!r}")
 
         self.file_name = f"{FILE_PREFIX}{file_uuid}.{file_extension}"
         self.file_content = file_content
diff --git a/kroki/config.py b/kroki/config.py
index 1077eb0..58278e8 100644
--- a/kroki/config.py
+++ b/kroki/config.py
@@ -7,8 +7,11 @@
 
 
 class DeprecatedDownloadImagesCompat(config_options.Deprecated):
-    def pre_validation(self, config: "KrokiPluginConfig", key_name: str) -> None:
+    def pre_validation(self, config: MkDocsBaseConfig, key_name: str) -> None:
         """Set `HttpMethod: 'POST'`, if enabled"""
+        if not isinstance(config, KrokiPluginConfig):
+            return
+
         if config.get(key_name) is None:
             return
 
diff --git a/kroki/diagram_types.py b/kroki/diagram_types.py
index a9b04f2..8e41cbc 100644
--- a/kroki/diagram_types.py
+++ b/kroki/diagram_types.py
@@ -1,11 +1,13 @@
 from collections import ChainMap
 from typing import ClassVar
 
+from mkdocs.exceptions import PluginError
+
 from kroki.logging import log
 
 
 class KrokiDiagramTypes:
-    _kroki_base: ClassVar[dict[str, list[str]]] = {
+    _base_diagrams: ClassVar[dict[str, list[str]]] = {
         "bytefield": ["svg"],
         "ditaa": ["png", "svg"],
         "erd": ["png", "svg", "jpeg", "pdf"],
@@ -27,7 +29,7 @@ class KrokiDiagramTypes:
         "wireviz": ["png", "svg"],
     }
 
-    _kroki_blockdiag: ClassVar[dict[str, list[str]]] = {
+    _blockdiag: ClassVar[dict[str, list[str]]] = {
         "blockdiag": ["png", "svg", "pdf"],
         "seqdiag": ["png", "svg", "pdf"],
         "actdiag": ["png", "svg", "pdf"],
@@ -36,19 +38,19 @@ class KrokiDiagramTypes:
         "rackdiag": ["png", "svg", "pdf"],
     }
 
-    _kroki_bpmn: ClassVar[dict[str, list[str]]] = {
+    _bpmn: ClassVar[dict[str, list[str]]] = {
         "bpmn": ["svg"],
     }
 
-    _kroki_excalidraw: ClassVar[dict[str, list[str]]] = {
+    _excalidraw: ClassVar[dict[str, list[str]]] = {
         "excalidraw": ["svg"],
     }
 
-    _kroki_mermaid: ClassVar[dict[str, list[str]]] = {
+    _mermaid: ClassVar[dict[str, list[str]]] = {
         "mermaid": ["png", "svg"],
     }
 
-    _kroki_diagramsnet: ClassVar[dict[str, list[str]]] = {
+    _diagramsnet: ClassVar[dict[str, list[str]]] = {
         "diagramsnet": ["svg"],
     }
 
@@ -66,39 +68,60 @@ def __init__(
     ):
         self._fence_prefix = fence_prefix
 
-        kroki_types = ChainMap(
-            self._kroki_base,
-            self._kroki_blockdiag if blockdiag_enabled else {},
-            self._kroki_bpmn if bpmn_enabled else {},
-            self._kroki_excalidraw if excalidraw_enabled else {},
-            self._kroki_mermaid if mermaid_enabled else {},
-            self._kroki_diagramsnet if diagramsnet_enabled else {},
+        diagram_type_file_ext_map = ChainMap(
+            self._base_diagrams,
+            self._blockdiag if blockdiag_enabled else {},
+            self._bpmn if bpmn_enabled else {},
+            self._excalidraw if excalidraw_enabled else {},
+            self._mermaid if mermaid_enabled else {},
+            self._diagramsnet if diagramsnet_enabled else {},
+        )
+
+        self._file_ext_mapping: dict[str, str] = self._get_file_ext_mapping(
+            diagram_type_file_ext_map, file_types, file_type_overrides
         )
 
-        self._kroki_types_supporting_file = {}
+        log.debug("File and Diagram types configured: %s", self._file_ext_mapping)
 
-        for kroki_type, kroki_file_types in kroki_types.items():
-            kroki_file_type = next(filter(lambda file: file in kroki_file_types, file_types), None)
-            if kroki_file_type is not None:
-                self._kroki_types_supporting_file[kroki_type] = next(
-                    filter(lambda file: file in kroki_file_types, file_types), None
+    def _get_file_ext_mapping(
+        self,
+        diagram_type_file_ext_map: ChainMap[str, list[str]],
+        file_types: list[str],
+        file_type_overrides: dict[str, str],
+    ) -> dict[str, str]:
+        def get_file_type(diagram_type: str) -> str:
+            supported_file_types = diagram_type_file_ext_map[diagram_type]
+            file_type_override = file_type_overrides.get(diagram_type)
+            if file_type_override is not None:
+                if file_type_override not in supported_file_types:
+                    err_msg = (
+                        f"{diagram_type}: {file_type_override} not in supported file types: " f"{supported_file_types}"
+                    )
+                    raise PluginError(err_msg)
+                return file_type_override
+
+            target_file_type = next((t for t in file_types if t in supported_file_types), None)
+            if target_file_type is None:
+                err_msg = (
+                    f"{diagram_type}: Not able to satisfy any of {file_types}, "
+                    f"supported file types: {supported_file_types}"
                 )
+                raise PluginError(err_msg)
 
-        for kroki_type, kroki_file_type in file_type_overrides.items():
-            self._kroki_types_supporting_file[kroki_type] = kroki_file_type
+            return target_file_type
 
-        log.debug("File and Diagram types configured: %s", self._kroki_types_supporting_file)
+        return {diagram_type: get_file_type(diagram_type) for diagram_type in diagram_type_file_ext_map}
 
     def get_file_ext(self, kroki_type: str) -> str:
-        return self._kroki_types_supporting_file[kroki_type]
+        return self._file_ext_mapping[kroki_type]
 
-    def get_kroki_type(self, block_type: None | str) -> None | str:
+    def get_kroki_type(self, block_type: None | str) -> str | None:
         if block_type is None:
-            return
+            return None
         if not block_type.startswith(self._fence_prefix):
-            return
-        kroki_type = block_type.removeprefix(self._fence_prefix).lower()
-        if kroki_type not in self._kroki_types_supporting_file:
-            return
+            return None
+        diagram_type = block_type.removeprefix(self._fence_prefix).lower()
+        if diagram_type not in self._file_ext_mapping:
+            return None
 
-        return kroki_type
+        return diagram_type
diff --git a/kroki/render.py b/kroki/render.py
index 05b97f8..fb06278 100644
--- a/kroki/render.py
+++ b/kroki/render.py
@@ -22,7 +22,8 @@ def _get_media_type(self, file_ext: str) -> str:
             case "pdf":
                 return "application/pdf"
             case _:
-                raise NotImplementedError(file_ext)
+                err_msg = f"Not implemented: '{file_ext}"
+                raise PluginError(err_msg)
 
     def _image_response(self, image_src: ImageSrc) -> str:
         media_type = self._get_media_type(image_src.file_ext)
diff --git a/pyproject.toml b/pyproject.toml
index 73fb328..6a457a0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,7 +28,6 @@ classifiers = [
     "License :: OSI Approved :: MIT License",
     "Programming Language :: Python",
     "Programming Language :: Python :: 3 :: Only",
-    "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
@@ -36,7 +35,7 @@ classifiers = [
 dependencies = [
     "mkdocs>=1.5.0",
     "requests>=2.27.0",
-    "result",
+    "result>=0.17.0",
 ]
 
 [project.entry-points."mkdocs.plugins"]
@@ -68,6 +67,8 @@ include = [
 [tool.hatch.envs.test]
 template = "hatch-test"
 [tool.hatch.envs.test.env-vars]
+# start local test kroki:
+#   docker-compose up
 KROKI_SERVER_URL = "http://localhost:8080"
 
 [tool.hatch.envs.hatch-test]
@@ -87,3 +88,15 @@ cov-report = [
     "coverage xml",
     "coverage report --omit='tests/*'",
 ]
+
+[tool.hatch.envs.types]
+template = "hatch-test"
+extra-dependencies = [
+  "mypy",
+  "types-PyYAML",
+  "types-beautifulsoup4",
+  "types-requests",
+  "types-babel",
+]
+[tool.hatch.envs.types.scripts]
+check = "mypy --install-types --non-interactive {args:kroki tests}"
diff --git a/tests/data/happy_path/docs/assets/diagram.plantuml b/tests/data/happy_path/docs/assets/diagram.plantuml
new file mode 100644
index 0000000..a7b4074
--- /dev/null
+++ b/tests/data/happy_path/docs/assets/diagram.plantuml
@@ -0,0 +1,3 @@
+@startuml
+Bob -> Alice : hello
+@enduml
diff --git a/tests/data/happy_path/docs/index.md b/tests/data/happy_path/docs/index.md
index 400bcd1..1c33850 100644
--- a/tests/data/happy_path/docs/index.md
+++ b/tests/data/happy_path/docs/index.md
@@ -1,5 +1,7 @@
 # Test
 
+## inline
+
 ```c4plantuml
 !include <C4/C4_Context>
 !include <C4/C4_Container>
@@ -29,3 +31,9 @@ Rel(site_host, db, "read")
 
 Rel(site_host, reader, "serve")
 ```
+
+## from file
+
+```plantuml
+@from_file:assets/diagram.plantuml
+```
diff --git a/tests/test_errors.py b/tests/test_errors.py
index 52266a5..3c26584 100644
--- a/tests/test_errors.py
+++ b/tests/test_errors.py
@@ -4,56 +4,66 @@
 from tests.utils import MkDocsHelper, get_expected_log_line
 
 
+def _assert_error_block(err_msg: str, index_html: str):
+    index_soup = bs4.BeautifulSoup(index_html)
+    details_tag = index_soup.find("details")
+    assert isinstance(details_tag, bs4.Tag), "Error message container not in resulting HTML"
+    summary_tag = details_tag.summary
+    assert isinstance(summary_tag, bs4.Tag), "Error message container has no summary element"
+    assert err_msg in summary_tag.text
+
+
 @pytest.mark.usefixtures("kroki_timeout")
 def test_request_timeout() -> None:
+    # Arrange
     with MkDocsHelper("happy_path") as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
-
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 0
         assert get_expected_log_line("Request error") in result.output
         with open(mkdocs_helper.test_dir / "site/index.html") as index_html_file:
-            index_soup = bs4.BeautifulSoup(index_html_file.read())
-            assert "Request error" in index_soup.find("details").summary.text
+            _assert_error_block("Request error", index_html_file.read())
 
 
 @pytest.mark.usefixtures("kroki_bad_request")
 def test_request_bad_request() -> None:
+    # Arrange
     with MkDocsHelper("happy_path") as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
-
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 0
         assert get_expected_log_line("Diagram error!") in result.output
         with open(mkdocs_helper.test_dir / "site/index.html") as index_html_file:
-            index_soup = bs4.BeautifulSoup(index_html_file.read())
-            assert "Diagram error!" in index_soup.find("details").summary.text
+            _assert_error_block("Diagram error!", index_html_file.read())
 
 
 @pytest.mark.usefixtures("kroki_is_a_teapot")
 def test_request_other_error() -> None:
+    # Arrange
     with MkDocsHelper("happy_path") as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
-
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 0
         assert get_expected_log_line("Could not retrieve image data") in result.output
         with open(mkdocs_helper.test_dir / "site/index.html") as index_html_file:
-            index_soup = bs4.BeautifulSoup(index_html_file.read())
-            assert "Could not retrieve image data" in index_soup.find("details").summary.text
+            _assert_error_block("Could not retrieve image data", index_html_file.read())
 
 
 @pytest.mark.usefixtures("kroki_dummy")
-def test_missing_file_from() -> None:
+def test_missing_from_file() -> None:
+    # Arrange
     with MkDocsHelper("missing_from_file") as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 0
         assert get_expected_log_line("Can't read file:") in result.output
         with open(mkdocs_helper.test_dir / "site/index.html") as index_html_file:
-            index_soup = bs4.BeautifulSoup(index_html_file.read())
-            assert "Can't read file: " in index_soup.find("details").summary.text
+            _assert_error_block("Can't read file: ", index_html_file.read())
diff --git a/tests/test_errors_fail_fast.py b/tests/test_errors_fail_fast.py
index 493facb..e3a8d01 100644
--- a/tests/test_errors_fail_fast.py
+++ b/tests/test_errors_fail_fast.py
@@ -5,12 +5,13 @@
 
 @pytest.mark.usefixtures("kroki_timeout")
 def test_request_timeout() -> None:
+    # Arrange
     with MkDocsHelper("happy_path") as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
         mkdocs_helper.enable_fail_fast()
-
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 1
         assert get_expected_log_line("Request error") in result.output
         assert "Aborted with a BuildError!" in result.output
@@ -18,12 +19,13 @@ def test_request_timeout() -> None:
 
 @pytest.mark.usefixtures("kroki_bad_request")
 def test_request_bad_request() -> None:
+    # Arrange
     with MkDocsHelper("happy_path") as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
         mkdocs_helper.enable_fail_fast()
-
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 1
         assert get_expected_log_line("Diagram error!") in result.output
         assert "Aborted with a BuildError!" in result.output
@@ -31,24 +33,26 @@ def test_request_bad_request() -> None:
 
 @pytest.mark.usefixtures("kroki_is_a_teapot")
 def test_request_other_error() -> None:
+    # Arrange
     with MkDocsHelper("happy_path") as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
         mkdocs_helper.enable_fail_fast()
-
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 1
         assert get_expected_log_line("Could not retrieve image data") in result.output
         assert "Aborted with a BuildError!" in result.output
 
 
 @pytest.mark.usefixtures("kroki_dummy")
-def test_missing_file_from() -> None:
+def test_missing_from_file() -> None:
+    # Arrange
     with MkDocsHelper("missing_from_file") as mkdocs_helper:
         mkdocs_helper.enable_fail_fast()
-
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 1
         assert get_expected_log_line("Can't read file:") in result.output
         assert "Aborted with a BuildError!" in result.output
diff --git a/tests/test_fences.py b/tests/test_fences.py
index dceade2..5359d83 100644
--- a/tests/test_fences.py
+++ b/tests/test_fences.py
@@ -1,4 +1,4 @@
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 
 import pytest
 from pytest_mock import MockerFixture
@@ -11,9 +11,9 @@
 @dataclass
 class StubInput:
     page_data: str
-    expected_code_block_data: str | None = None
-    epxected_options: dict | None = None
-    expected_kroki_type: str | None = None
+    expected_code_block_data: str = ""
+    epxected_options: dict = field(default_factory=dict)
+    expected_kroki_type: str = ""
 
 
 TEST_CASES = {
@@ -26,7 +26,6 @@ class StubInput:
 """,
         expected_code_block_data="stuff containing ```\n\n",
         expected_kroki_type="plantuml",
-        epxected_options={},
     ),
     "https://pandoc.org/MANUAL.html#fenced-code-blocks": StubInput(
         page_data="""~~~~~~~~~~~~~~~~ mermaid
@@ -36,7 +35,6 @@ class StubInput:
 ~~~~~~~~~~~~~~~~""",
         expected_code_block_data="~~~~~~~~~~\ncode including tildes\n~~~~~~~~~~\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-119": StubInput(
         page_data="""
@@ -47,7 +45,6 @@ class StubInput:
 """,
         expected_code_block_data="<\n >\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-120": StubInput(
         page_data="""
@@ -58,7 +55,6 @@ class StubInput:
 """,
         expected_code_block_data="<\n >\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-122": StubInput(
         page_data="""
@@ -69,7 +65,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n~~~\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-123": StubInput(
         page_data="""
@@ -80,7 +75,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n```\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-125": StubInput(
         page_data="""
@@ -91,7 +85,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n~~~\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-129": StubInput(
         page_data="""
@@ -102,7 +95,6 @@ class StubInput:
 """,
         expected_code_block_data="\n\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-130": StubInput(
         page_data="""
@@ -111,7 +103,6 @@ class StubInput:
 """,
         expected_code_block_data="",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-147": StubInput(
         page_data="""
@@ -121,7 +112,6 @@ class StubInput:
 """,
         expected_code_block_data="``` aaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
 }
 
@@ -136,7 +126,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n  aaa\naaa\n",  # "aaa\naaa\naaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-133": StubInput(
         page_data="""
@@ -148,7 +137,15 @@ class StubInput:
 """,
         expected_code_block_data=" aaa\n  aaa\naaa\n",  # "aaa\n aaa\naaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
+    ),
+    "https://spec.commonmark.org/0.31.2/#example-134": StubInput(
+        page_data="""
+    ``` mermaid
+    aaa
+    ```
+""",
+        expected_code_block_data="aaa\n",  # should not be replaced..
+        expected_kroki_type="mermaid",
     ),
 }
 
@@ -161,7 +158,6 @@ class StubInput:
 """,
         expected_code_block_data="foo\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-124": StubInput(
         page_data="""
@@ -172,7 +168,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n```\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-126": StubInput(
         page_data="""
@@ -180,7 +175,6 @@ class StubInput:
 """,
         expected_code_block_data="\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-127": StubInput(
         page_data="""
@@ -191,7 +185,6 @@ class StubInput:
 """,
         expected_code_block_data="\n```\naaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-128": StubInput(
         page_data="""
@@ -202,7 +195,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-131": StubInput(
         page_data="""
@@ -213,17 +205,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\naaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
-    ),
-    "https://spec.commonmark.org/0.31.2/#example-134": StubInput(
-        page_data="""
-    ``` mermaid
-    aaa
-    ```,
-            expected_code_block_data="aaa\n",  # should not be replaced..
-        expected_kroki_type="mermaid",
-        epxected_options={},
-"""
     ),
     "https://spec.commonmark.org/0.31.2/#example-135": StubInput(
         page_data="""
@@ -233,7 +214,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-136": StubInput(
         page_data="""
@@ -243,7 +223,6 @@ class StubInput:
 """,
         expected_code_block_data="aaa\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-140": StubInput(
         page_data="""
@@ -255,7 +234,6 @@ class StubInput:
 """,
         expected_code_block_data="bar\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-141": StubInput(
         page_data="""
@@ -268,7 +246,6 @@ class StubInput:
 """,
         expected_code_block_data="bar\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
     "https://spec.commonmark.org/0.31.2/#example-146": StubInput(
         page_data="""
@@ -278,7 +255,6 @@ class StubInput:
 """,
         expected_code_block_data="foo\n",
         expected_kroki_type="mermaid",
-        epxected_options={},
     ),
 }
 
@@ -289,13 +265,13 @@ class StubInput:
     + [pytest.param(v, id=k) for k, v in TEST_CASES_NOT_COMPLYING.items()],
 )
 def test_fences(test_data: StubInput, mock_kroki_diagram_types: KrokiDiagramTypes, mocker: MockerFixture) -> None:
+    # Arrange
     parser = MarkdownParser("", mock_kroki_diagram_types)
-
     callback_stub = mocker.stub()
     context_stub = mocker.stub()
-
+    # Act
     parser.replace_kroki_blocks(test_data.page_data, callback_stub, context_stub)
-
+    # Assert
     callback_stub.assert_called_once_with(
         KrokiImageContext(
             kroki_type=test_data.expected_kroki_type,
@@ -310,11 +286,11 @@ def test_fences(test_data: StubInput, mock_kroki_diagram_types: KrokiDiagramType
 def test_fences_not_supported(
     test_data: StubInput, mock_kroki_diagram_types: KrokiDiagramTypes, mocker: MockerFixture
 ) -> None:
+    # Arrange
     parser = MarkdownParser("", mock_kroki_diagram_types)
-
     callback_stub = mocker.stub()
     context_stub = mocker.stub()
-
+    # Act
     parser.replace_kroki_blocks(test_data.page_data, callback_stub, context_stub)
-
+    # Assert
     callback_stub.assert_not_called()
diff --git a/tests/test_happy_path.py b/tests/test_happy_path.py
new file mode 100644
index 0000000..50bb6a6
--- /dev/null
+++ b/tests/test_happy_path.py
@@ -0,0 +1,22 @@
+import bs4
+import pytest
+
+from tests.utils import MkDocsHelper
+
+
+@pytest.mark.usefixtures("kroki_dummy")
+def test_happy_path() -> None:
+    # Arrange
+    with MkDocsHelper("happy_path") as mkdocs_helper:
+        mkdocs_helper.set_http_method("POST")
+        # Act
+        result = mkdocs_helper.invoke_build()
+        # Assert
+        assert result.exit_code == 0
+        with open(mkdocs_helper.test_dir / "site/index.html") as index_html_file:
+            index_html = index_html_file.read()
+
+        index_soup = bs4.BeautifulSoup(index_html)
+        img_tags = index_soup.find_all(attrs={"name": "Kroki"})
+
+        assert len(img_tags) == 2
diff --git a/tests/test_nested.py b/tests/test_nested.py
index 9012d99..640e4a8 100644
--- a/tests/test_nested.py
+++ b/tests/test_nested.py
@@ -6,6 +6,7 @@
 
 @pytest.mark.usefixtures("kroki_dummy")
 def test_block_inside_html() -> None:
+    # Arrange
     with MkDocsTemplateHelper("""
 <details>
     <summary><u>Show Sequence diagram...</u></summary>
@@ -21,8 +22,9 @@ def test_block_inside_html() -> None:
 ```
 """) as mkdocs_helper:
         mkdocs_helper.set_http_method("POST")
+        # Act
         result = mkdocs_helper.invoke_build()
-
+        # Assert
         assert result.exit_code == 0, f"exit code {result.exit_code}, expected 0"
         with open(mkdocs_helper.test_dir / "site/index.html") as index_html:
             index_soup = bs4.BeautifulSoup(index_html.read())
diff --git a/tests/utils.py b/tests/utils.py
index 664bf6e..a40f430 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -5,7 +5,7 @@
 from contextlib import AbstractContextManager
 from pathlib import Path
 from string import Template
-from typing import Literal
+from typing import Final, Literal
 
 import yaml
 from click.testing import CliRunner, Result
@@ -15,7 +15,7 @@
 from tests.compat import chdir
 
 
-def get_expected_log_line(log_msg) -> str:
+def get_expected_log_line(log_msg: str) -> str:
     return f"{log.prefix}: {log_msg}"
 
 
@@ -25,62 +25,67 @@ def __init__(self) -> None:
 
 
 class MkDocsHelper(AbstractContextManager):
+    class Context:
+        def __init__(self, test_dir: Path) -> None:
+            self.test_dir: Final[Path] = test_dir
+            self.config_file_path: Final[Path] = test_dir / "mkdocs.yml"
+            with open(self.test_dir / "mkdocs.yml") as file:
+                self.config_file = yaml.safe_load(file)
+
+        def _dump_config(self) -> None:
+            with open(self.config_file_path, mode="w") as file:
+                yaml.safe_dump(self.config_file, file)
+
+        def _get_plugin_config_entry(self) -> dict:
+            for plugin_entry in self.config_file["plugins"]:
+                if "kroki" in plugin_entry:
+                    return plugin_entry["kroki"]
+            raise NoPluginEntryError
+
+        def enable_fail_fast(self) -> None:
+            self._get_plugin_config_entry()["FailFast"] = True
+
+        def set_http_method(self, method: Literal["GET", "POST"]) -> None:
+            self._get_plugin_config_entry()["HttpMethod"] = method
+
+        def set_fence_prefix(self, fence_prefix: str) -> None:
+            self._get_plugin_config_entry()["FencePrefix"] = fence_prefix
+
+        def invoke_build(self) -> Result:
+            self._dump_config()
+            runner = CliRunner()
+            with chdir(self.test_dir):
+                return runner.invoke(build_command)
+
     def __init__(self, test_case: str) -> None:
-        self.config_file = None
         self.test_case = test_case
         self.test_dir = Path(tempfile.mkdtemp())
-        self._copy_test_case()
 
     def _copy_test_case(self) -> None:
         # equals to `../data`, using current source file as a pin
         data_dir = pathlib.Path(os.path.realpath(__file__)).parent / "data"
         shutil.copytree(data_dir / self.test_case, self.test_dir, dirs_exist_ok=True)
 
-    def _load_config(self) -> None:
-        with open(self.test_dir / "mkdocs.yml") as file:
-            self.config_file = yaml.safe_load(file)
-
-    def _dump_config(self) -> None:
-        with open(self.test_dir / "mkdocs.yml", mode="w") as file:
-            yaml.safe_dump(self.config_file, file)
-
-    def __enter__(self) -> "MkDocsHelper":
-        self._load_config()
-
-        return self
+    def __enter__(self) -> Context:
+        self._copy_test_case()
+        return MkDocsHelper.Context(self.test_dir)
 
     def __exit__(self, *_args) -> None:
         shutil.rmtree(self.test_dir)
 
-    def _get_plugin_config_entry(self) -> dict:
-        for plugin_entry in self.config_file["plugins"]:
-            if "kroki" in plugin_entry:
-                return plugin_entry["kroki"]
-        raise NoPluginEntryError
-
-    def enable_fail_fast(self) -> None:
-        self._get_plugin_config_entry()["FailFast"] = True
-
-    def set_http_method(self, method: Literal["GET", "POST"]) -> None:
-        self._get_plugin_config_entry()["HttpMethod"] = method
-
-    def set_fence_prefix(self, fence_prefix: str) -> None:
-        self._get_plugin_config_entry()["FencePrefix"] = fence_prefix
-
-    def invoke_build(self) -> Result:
-        self._dump_config()
-        runner = CliRunner()
-        with chdir(self.test_dir):
-            return runner.invoke(build_command)
-
 
 class MkDocsTemplateHelper(MkDocsHelper):
-    def _substitute_code_block(self, code_block: str):
+    def _substitute_code_block(self):
         with open(self.test_dir / "docs/index.md") as in_file:
             file_content = Template(in_file.read())
             with open(self.test_dir / "docs/index.md", "w") as out_file:
-                out_file.write(file_content.substitute(code_block=code_block))
+                out_file.write(file_content.substitute(code_block=self.code_block))
 
     def __init__(self, code_block: str) -> None:
         super().__init__("template")
-        self._substitute_code_block(code_block)
+        self.code_block = code_block
+
+    def __enter__(self) -> MkDocsHelper.Context:
+        context = super().__enter__()
+        self._substitute_code_block()
+        return context