diff --git a/__test__/readme-helper.unit.test.ts b/__test__/readme-helper.unit.test.ts
new file mode 100644
index 0000000..58d2a60
--- /dev/null
+++ b/__test__/readme-helper.unit.test.ts
@@ -0,0 +1,196 @@
+import {completeRelativeUrls} from '../src/readme-helper'
+
+describe('complete relative urls tests', () => {
+  const GITHUB_SERVER_URL = process.env['GITHUB_SERVER_URL']
+  const GITHUB_REPOSITORY = process.env['GITHUB_REPOSITORY']
+  const GITHUB_REF_NAME = process.env['GITHUB_REF_NAME']
+
+  const README_FILEPATH = './README.md'
+  const EXPECTED_REPOSITORY_URL = `${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}`
+  const EXPECTED_BLOB_URL = `${EXPECTED_REPOSITORY_URL}/blob/${GITHUB_REF_NAME}`
+  const EXPECTED_RAW_URL = `${EXPECTED_REPOSITORY_URL}/raw/${GITHUB_REF_NAME}`
+  
+  // known issues
+  test('reference-style links/image sources are not converted', async () => {
+    const content = ['table-of-content][toc]',
+      '',
+      '[toc]: #table-of-content "Table of content"'
+    ].join('\n')
+    expect(
+      completeRelativeUrls(content, README_FILEPATH, true, '')
+    ).toEqual(content)
+  })
+
+  test('links containing square brackets in the text fragment are not converted', async () => {
+    expect(
+      completeRelativeUrls('[[text with square brackets]](README.md)', README_FILEPATH, true, '')
+    ).toEqual('[[text with square brackets]](README.md)')
+  })
+
+  test('links containing square brackets in the text fragment are not converted', async () => {
+    expect(
+      completeRelativeUrls('`[text](README.md)`', README_FILEPATH, true, '')
+    ).toEqual(`\`[text](${EXPECTED_BLOB_URL}/README.md)\``)
+  })
+
+  // misc
+  test('do not change content when disabled', async () => {
+    expect(
+      completeRelativeUrls('[text](README.md)', README_FILEPATH, false, '')
+    ).toEqual('[text](README.md)')
+  })
+
+  test('do not change link with mailto protocol', async () => {
+    expect(
+      completeRelativeUrls('[text](mailto:mail@example.com)', README_FILEPATH, true, '')
+    ).toEqual(`[text](mailto:mail@example.com)`)
+  })
+
+  test('do not change link with ftp protocol', async () => {
+    expect(
+      completeRelativeUrls('[text](ftp://example.com)', README_FILEPATH, true, '')
+    ).toEqual(`[text](ftp://example.com)`)
+  })
+
+  test('do not change link with http protocol', async () => {
+    expect(
+      completeRelativeUrls('[text](http://example.com)', README_FILEPATH, true, '')
+    ).toEqual(`[text](http://example.com)`)
+  })
+
+  test('do not change link with https protocol', async () => {
+    expect(
+      completeRelativeUrls('[text](https://example.com)', README_FILEPATH, true, '')
+    ).toEqual(`[text](https://example.com)`)
+  })
+
+  test('do not change link with protocol-like beginning', async () => {
+    expect(
+      completeRelativeUrls('[text](abc://example.com)', README_FILEPATH, true, '')
+    ).toEqual(`[text](abc://example.com)`)
+  })
+
+  test('do not change image from absolute source with absolute link', async () => {
+    expect(
+      completeRelativeUrls('[![alttext](https://example.com/image.svg)](https://example.com/image.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`[![alttext](https://example.com/image.svg)](https://example.com/image.svg)`)
+  })
+
+  // anchors
+  test('anchor referencing the current document', async () => {
+    expect(
+      completeRelativeUrls('[text](#relative-anchor)', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/README.md#relative-anchor)`)
+  })
+
+  test('anchor referencing the current document with a title', async () => {
+    expect(
+      completeRelativeUrls('[text](#relative-anchor "the anchor (a title)")', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/README.md#relative-anchor "the anchor (a title)")`)
+  })
+
+  test('anchor referencing the current document with a title and unicode', async () => {
+    expect(
+      completeRelativeUrls('[text with 🌬](#relative-anchor "the anchor (a title with 🌬)")', README_FILEPATH, true, '')
+    ).toEqual(`[text with 🌬](${EXPECTED_BLOB_URL}/README.md#relative-anchor "the anchor (a title with 🌬)")`)
+  })
+
+  test('anchor referencing another document', async () => {
+    expect(
+      completeRelativeUrls('[text](OTHER.md#absolute-anchor)', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/OTHER.md#absolute-anchor)`)
+  })
+
+  test('anchor referencing another document with a title', async () => {
+    expect(
+      completeRelativeUrls('[text](OTHER.md#absolute-anchor "the anchor (a title)")', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/OTHER.md#absolute-anchor "the anchor (a title)")`)
+  })
+
+  test('anchor with image referencing the current document', async () => {
+    expect(
+      completeRelativeUrls('[![alttext](image.svg)](#absolute-anchor "the anchor (a title)")', README_FILEPATH, true, 'svg')
+    ).toEqual(`[![alttext](${EXPECTED_RAW_URL}/image.svg)](${EXPECTED_BLOB_URL}/README.md#absolute-anchor "the anchor (a title)")`)
+  })
+
+  test('anchor with image referencing another document', async () => {
+    expect(
+      completeRelativeUrls('[![alttext](image.svg)](OTHER.md#absolute-anchor "the anchor (a title)")', README_FILEPATH, true, 'svg')
+    ).toEqual(`[![alttext](${EXPECTED_RAW_URL}/image.svg)](${EXPECTED_BLOB_URL}/OTHER.md#absolute-anchor "the anchor (a title)")`)
+  })
+
+  // documents
+  test('text document', async () => {
+    expect(
+      completeRelativeUrls('[text](document.yaml)', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/document.yaml)`)
+  })
+
+  test('pdf document', async () => {
+    expect(
+      completeRelativeUrls('[text](document.pdf)', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/document.pdf)`)
+  })
+
+  test('document with a title', async () => {
+    expect(
+      completeRelativeUrls('[text](document.pdf "the document (a title)")', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/document.pdf "the document (a title)")`)
+  })
+
+  test('document with a title and unicode', async () => {
+    expect(
+      completeRelativeUrls('[text with 🌬](document.pdf "the document (a title with 🌬)")', README_FILEPATH, true, '')
+    ).toEqual(`[text with 🌬](${EXPECTED_BLOB_URL}/document.pdf "the document (a title with 🌬)")`)
+  })
+
+  // images
+  test('image with supported file extension', async () => {
+    expect(
+      completeRelativeUrls('![alttext](image.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`![alttext](${EXPECTED_RAW_URL}/image.svg)`)
+  })
+
+  test('image with unsupported file extension', async () => {
+    expect(
+      completeRelativeUrls('![alttext](image.svg)', README_FILEPATH, true, 'jpeg')
+    ).toEqual(`![alttext](${EXPECTED_BLOB_URL}/image.svg)`)
+  })
+
+  test('image without alternate text', async () => {
+    expect(
+      completeRelativeUrls('![](image.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`![](${EXPECTED_RAW_URL}/image.svg)`)
+  })
+
+  test('image with a title', async () => {
+    expect(
+      completeRelativeUrls('![alttext](image.svg "the image (a title)")', README_FILEPATH, true, 'svg')
+    ).toEqual(`![alttext](${EXPECTED_RAW_URL}/image.svg "the image (a title)")`)
+  })
+
+  test('image with relative link', async () => {
+    expect(
+      completeRelativeUrls('[![alttext](image.svg)](image.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`[![alttext](${EXPECTED_RAW_URL}/image.svg)](${EXPECTED_BLOB_URL}/image.svg)`)
+  })
+
+  test('image with a title, unicode and relative link', async () => {
+    expect(
+      completeRelativeUrls('[![alttext with 🌬](image.🌬.svg "the image.🌬.svg (a title)")](image.🌬.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`[![alttext with 🌬](${EXPECTED_RAW_URL}/image.🌬.svg "the image.🌬.svg (a title)")](${EXPECTED_BLOB_URL}/image.🌬.svg)`)
+  })
+
+  test('image from absolute source with relative link', async () => {
+    expect(
+      completeRelativeUrls('[![alttext](https://example.com/image.svg)](image.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`[![alttext](https://example.com/image.svg)](${EXPECTED_BLOB_URL}/image.svg)`)
+  })
+
+  test('image with absolute link', async () => {
+    expect(
+      completeRelativeUrls('[![alttext](image.svg)](https://example.com/image.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`[![alttext](${EXPECTED_RAW_URL}/image.svg)](https://example.com/image.svg)`)
+  })
+
+})
diff --git a/dist/index.js b/dist/index.js
index 7916085..e7114ca 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -311,7 +311,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 Object.defineProperty(exports, "__esModule", ({ value: true }));
-exports.getReadmeContent = exports.ENABLE_URL_COMPLETION_DEFAULT = exports.IMAGE_EXTENSIONS_DEFAULT = exports.README_FILEPATH_DEFAULT = void 0;
+exports.completeRelativeUrls = exports.getReadmeContent = exports.ENABLE_URL_COMPLETION_DEFAULT = exports.IMAGE_EXTENSIONS_DEFAULT = exports.README_FILEPATH_DEFAULT = void 0;
 const core = __importStar(__nccwpck_require__(2186));
 const fs = __importStar(__nccwpck_require__(7147));
 exports.README_FILEPATH_DEFAULT = './README.md';
@@ -327,19 +327,24 @@ function getReadmeContent(readmeFilepath, enableUrlCompletion, imageExtensions)
         let readmeContent = yield fs.promises.readFile(readmeFilepath, {
             encoding: 'utf8'
         });
-        if (enableUrlCompletion) {
-            // Make relative urls absolute
-            const rules = [
-                ...getRelativeReadmeAnchorsRules(readmeFilepath),
-                ...getRelativeImageUrlRules(imageExtensions),
-                ...getRelativeUrlRules()
-            ];
-            readmeContent = applyRules(rules, readmeContent);
-        }
+        readmeContent = completeRelativeUrls(readmeContent, readmeFilepath, enableUrlCompletion, imageExtensions);
         return readmeContent;
     });
 }
 exports.getReadmeContent = getReadmeContent;
+function completeRelativeUrls(readmeContent, readmeFilepath, enableUrlCompletion, imageExtensions) {
+    if (enableUrlCompletion) {
+        // Make relative urls absolute
+        const rules = [
+            ...getRelativeReadmeAnchorsRules(readmeFilepath),
+            ...getRelativeImageUrlRules(imageExtensions),
+            ...getRelativeUrlRules()
+        ];
+        readmeContent = applyRules(rules, readmeContent);
+    }
+    return readmeContent;
+}
+exports.completeRelativeUrls = completeRelativeUrls;
 function applyRules(rules, readmeContent) {
     rules.forEach(rule => {
         const combinedRegex = `${rule.left.source}[(]${rule.url.source}[)]`;
diff --git a/jest.config.js b/jest.config.js
index 14e44f9..a81d050 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -9,3 +9,8 @@ module.exports = {
   },
   verbose: true
 }
+process.env = Object.assign(process.env, {
+  GITHUB_SERVER_URL: 'https://github.com',
+  GITHUB_REPOSITORY: 'peter-evans/dockerhub-description',
+  GITHUB_REF_NAME: 'main'
+})
\ No newline at end of file
diff --git a/package.json b/package.json
index 823b18e..22a521f 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
     "format": "prettier --write '**/*.ts'",
     "format-check": "prettier --check '**/*.ts'",
     "lint": "eslint src/**/*.ts",
-    "test": "jest --passWithNoTests"
+    "test": "jest"
   },
   "repository": {
     "type": "git",
diff --git a/src/readme-helper.ts b/src/readme-helper.ts
index d5aface..0ce6c6d 100644
--- a/src/readme-helper.ts
+++ b/src/readme-helper.ts
@@ -35,6 +35,22 @@ export async function getReadmeContent(
     encoding: 'utf8'
   })
 
+  readmeContent = completeRelativeUrls(
+    readmeContent,
+    readmeFilepath,
+    enableUrlCompletion,
+    imageExtensions
+  )
+
+  return readmeContent
+}
+
+export function completeRelativeUrls(
+  readmeContent: string,
+  readmeFilepath: string,
+  enableUrlCompletion: boolean,
+  imageExtensions: string
+): string {
   if (enableUrlCompletion) {
     readmeFilepath = readmeFilepath.replace(/^[.][/]/, '')