diff --git a/package-lock.json b/package-lock.json
index 312acb9..eb76c97 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -14,8 +14,10 @@
       },
       "devDependencies": {
         "@jest/globals": "^29.7.0",
+        "@types/mock-fs": "^4.13.4",
         "@types/node": "^20.8.2",
         "jest": "^29.7.0",
+        "mock-fs": "^5.2.0",
         "prettier": "^3.0.3",
         "ts-jest": "^29.1.2",
         "typescript": "^5.2.2",
@@ -1343,6 +1345,15 @@
         "@types/istanbul-lib-report": "*"
       }
     },
+    "node_modules/@types/mock-fs": {
+      "version": "4.13.4",
+      "resolved": "https://registry.npmjs.org/@types/mock-fs/-/mock-fs-4.13.4.tgz",
+      "integrity": "sha512-mXmM0o6lULPI8z3XNnQCpL0BGxPwx1Ul1wXYEPBGl4efShyxW2Rln0JOPEWGyZaYZMM6OVXM/15zUuFMY52ljg==",
+      "dev": true,
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/node": {
       "version": "20.12.11",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-20.12.11.tgz",
@@ -3199,6 +3210,15 @@
         "node": "*"
       }
     },
+    "node_modules/mock-fs": {
+      "version": "5.2.0",
+      "resolved": "https://registry.npmjs.org/mock-fs/-/mock-fs-5.2.0.tgz",
+      "integrity": "sha512-2dF2R6YMSZbpip1V1WHKGLNjr/k48uQClqMVb5H3MOvwc9qhYis3/IWbj02qIg/Y8MDXKFF4c5v0rxx2o6xTZw==",
+      "dev": true,
+      "engines": {
+        "node": ">=12.0.0"
+      }
+    },
     "node_modules/ms": {
       "version": "2.1.2",
       "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.2.tgz",
diff --git a/package.json b/package.json
index 2ea7380..a08170c 100644
--- a/package.json
+++ b/package.json
@@ -43,8 +43,10 @@
   },
   "devDependencies": {
     "@jest/globals": "^29.7.0",
+    "@types/mock-fs": "^4.13.4",
     "@types/node": "^20.8.2",
     "jest": "^29.7.0",
+    "mock-fs": "^5.2.0",
     "prettier": "^3.0.3",
     "ts-jest": "^29.1.2",
     "typescript": "^5.2.2",
diff --git a/src/utils.ts b/src/utils.ts
index 3509173..ec67afe 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -18,7 +18,7 @@ export function initializePluginConfig(
 }
 
 export function readJsonFile(file: string): any {
-    return JSON.parse(readFileSync(file, "utf-8")) || {};
+    return JSON.parse(readFileSync(file, "utf-8"));
 }
 
 export function isComposerRoot(file: string): boolean {
diff --git a/test/fixtures/projectComposerFile.json b/test/fixtures/composerProject/composer.json
similarity index 100%
rename from test/fixtures/projectComposerFile.json
rename to test/fixtures/composerProject/composer.json
diff --git a/test/fixtures/extensionComposerFile.json b/test/fixtures/composerProject/packages/composerExtension/composer.json
similarity index 100%
rename from test/fixtures/extensionComposerFile.json
rename to test/fixtures/composerProject/packages/composerExtension/composer.json
diff --git a/test/fixtures/composerProject/vendor/composer/installed.json b/test/fixtures/composerProject/vendor/composer/installed.json
new file mode 100644
index 0000000..ba375f0
--- /dev/null
+++ b/test/fixtures/composerProject/vendor/composer/installed.json
@@ -0,0 +1,5 @@
+{
+    "packages": [
+
+    ]
+}
diff --git a/test/fixtures/libraryComposerFile.json b/test/fixtures/composerProject/vendor/namespace/library/composer.json
similarity index 100%
rename from test/fixtures/libraryComposerFile.json
rename to test/fixtures/composerProject/vendor/namespace/library/composer.json
diff --git a/test/fixtures/nonComposerProject/typo3conf/ext/non_composer_extension/.gitkeep b/test/fixtures/nonComposerProject/typo3conf/ext/non_composer_extension/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/test/utils.test.ts b/test/utils.test.ts
index c85e9aa..e7bd24c 100644
--- a/test/utils.test.ts
+++ b/test/utils.test.ts
@@ -1,27 +1,76 @@
-import { describe, expect, test } from "@jest/globals";
-import { isComposerRoot } from "../src/utils";
+import { describe, expect, test, beforeAll, afterAll } from "@jest/globals";
+import { determineComposerRoot, isComposerRoot, readJsonFile } from "../src/utils";
 import { resolve } from "node:path";
+import mockFs from "mock-fs";
 
-describe("utils module", () => {
-    test("checks projectComposerFile.json to be valid root composer file", () => {
+beforeAll(() => {
+    mockFs({
+        "/path/to/fixtures": mockFs.load(resolve(__dirname, "fixtures"))
+    });
+})
+afterAll(() => {
+    mockFs.restore();
+})
+
+describe("isComposerRoot", () => {
+    test("checks project composer.json to be valid root composer file", () => {
         expect(
-            isComposerRoot(
-                resolve(__dirname, "fixtures/projectComposerFile.json"),
-            ),
+            isComposerRoot("/path/to/fixtures/composerProject/composer.json")
         ).toBe(true);
     });
-    test("checks extensionComposerFile.json to be invalid root composer file", () => {
+    test("checks extension composer.json to be invalid root composer file", () => {
         expect(
-            isComposerRoot(
-                resolve(__dirname, "fixtures/extensionComposerFile.json"),
-            ),
+            isComposerRoot("/path/to/fixtures/composerProject/packages/composerExtension/composer.json")
         ).toBe(false);
     });
-    test("checks libraryComposerFile.json to be invalid root composer file", () => {
+    test("checks library composer.json to be invalid root composer file", () => {
         expect(
-            isComposerRoot(
-                resolve(__dirname, "fixtures/libraryComposerFile.json"),
-            ),
+            isComposerRoot("/path/to/fixtures/composerProject/vendor/namespace/library/composer.json")
         ).toBe(false);
     });
 });
+
+describe("readJsonFile", () => {
+    test("reads composer.json as json", () => {
+        expect(
+            readJsonFile("/path/to/fixtures/composerProject/vendor/namespace/library/composer.json")
+        ).toEqual({"type": "library"});
+    });
+});
+
+describe("determineComposerRoot", () => {
+    test("determines composer root from extension path", () => {
+        expect(
+            determineComposerRoot("/path/to/fixtures/composerProject/packages/composerExtension")
+        ).toBe("/path/to/fixtures/composerProject");
+    });
+    test("determines composer root from library path", () => {
+        expect(
+            determineComposerRoot("/path/to/fixtures/composerProject/vendor/namespace/library")
+        ).toBe("/path/to/fixtures/composerProject");
+    });
+    test("determines composer root from root path", () => {
+        expect(
+            determineComposerRoot("/path/to/fixtures/composerProject")
+        ).toBe("/path/to/fixtures/composerProject");
+    });
+    test("determines composer root from other path", () => {
+        expect(
+            determineComposerRoot("/path/to/fixtures/composerProject/packages")
+        ).toBe("/path/to/fixtures/composerProject");
+    });
+
+    test("fail to determine composer root from extension path", () => {
+        expect(
+            determineComposerRoot("/path/to/fixtures/nonComposerProject/typo3conf/ext/non_composer_extension")
+        ).toBe("/path/to/fixtures/nonComposerProject/typo3conf/ext/non_composer_extension");
+    });
+    test("fail to determine composer root from extension path with fallback root specified", () => {
+        expect(
+            determineComposerRoot(
+                "/path/to/fixtures/nonComposerProject/typo3conf/ext/non_composer_extension",
+                "/path/to/fixtures/nonComposerProject",
+            )
+        ).toBe("/path/to/fixtures/nonComposerProject");
+    });
+});