diff --git a/frontend/src/app/[locale]/projects/[projectId]/runs/[runId]/RunEditor.tsx b/frontend/src/app/[locale]/projects/[projectId]/runs/[runId]/RunEditor.tsx
index 70b4ce8..b33c59d 100644
--- a/frontend/src/app/[locale]/projects/[projectId]/runs/[runId]/RunEditor.tsx
+++ b/frontend/src/app/[locale]/projects/[projectId]/runs/[runId]/RunEditor.tsx
@@ -25,7 +25,7 @@ import { testRunStatus } from '@/config/selection';
 import { RunType, RunCaseType, RunStatusCountType, RunMessages } from '@/types/run';
 import { CaseType } from '@/types/case';
 import { FolderType } from '@/types/folder';
-import { fetchRun, updateRun, fetchRunCases, updateRunCases } from '../runsControl';
+import { fetchRun, updateRun, fetchRunCases, updateRunCases, processRunCases } from '../runsControl';
 import { fetchFolders } from '../../folders/foldersControl';
 import { fetchCases } from '@/utils/caseControl';
 import { TokenContext } from '@/utils/TokenProvider';
@@ -171,50 +171,8 @@ export default function RunEditor({ projectId, runId, messages, locale }: Props)
       keys = Array.from(selectedKeys).map(Number);
     }
 
-    if (isInclude) {
-      // TODO fix and add unit test
-      setRunCases((prevRunCases) => {
-        const updatedRunCases = prevRunCases.map((runCase) => {
-          if (keys.includes(runCase.caseId) && runCase.editState === 'deleted') {
-            return { ...runCase, editState: 'changed' };
-          }
-          return runCase;
-        });
-
-        keys.forEach((caseId) => {
-          const existingRunCase = prevRunCases.find((runCase) => runCase.caseId === caseId);
-          if (!existingRunCase) {
-            updatedRunCases.push({
-              id: -1,
-              runId: Number(runId),
-              caseId: caseId,
-              status: -1,
-              editState: 'new',
-            });
-          }
-        });
-
-        return updatedRunCases;
-      });
-    } else {
-      setRunCases((prevRunCases) =>
-        prevRunCases
-          .filter((runCase) => {
-            // If editState is 'new', remove from the array
-            if (keys.includes(runCase.caseId) && runCase.editState === 'new') {
-              return false;
-            }
-            return true;
-          })
-          .map((runCase) => {
-            // If editState isn't 'new', set editState to 'deleted'.
-            if (keys.includes(runCase.caseId) && runCase.editState !== 'new') {
-              return { ...runCase, editState: 'deleted' };
-            }
-            return runCase;
-          })
-      );
-    }
+    const newRunCases = processRunCases(isInclude, keys, Number(runId), runCases);
+    setRunCases(newRunCases);
 
     const updatedTestCases = testcases.map((testcase) => {
       if (keys.includes(testcase.id)) {
diff --git a/frontend/src/app/[locale]/projects/[projectId]/runs/runsControl.test.ts b/frontend/src/app/[locale]/projects/[projectId]/runs/runsControl.test.ts
new file mode 100644
index 0000000..0074e0d
--- /dev/null
+++ b/frontend/src/app/[locale]/projects/[projectId]/runs/runsControl.test.ts
@@ -0,0 +1,41 @@
+import { describe, expect, test } from 'vitest';
+import { processRunCases } from './runsControl';
+import { RunCaseType } from '@/types/run';
+
+const initialRuncases: RunCaseType[] = [
+  { id: 1, runId: 1, caseId: 1, editState: 'notChanged', status: 0 },
+  { id: 2, runId: 1, caseId: 2, editState: 'notChanged', status: 0 },
+  { id: 3, runId: 1, caseId: 3, editState: 'notChanged', status: 0 },
+];
+
+describe('runsControl', () => {
+  test('Add test cases not yet included in the test run', () => {
+    const isInclude = true;
+    const keys: number[] = [4, 5];
+    const runId = 1;
+    const currentRunCases = [...initialRuncases];
+    const newRunCases = processRunCases(isInclude, keys, runId, currentRunCases);
+
+    expect(newRunCases).toStrictEqual([
+      { id: 1, runId: 1, caseId: 1, editState: 'notChanged', status: 0 },
+      { id: 2, runId: 1, caseId: 2, editState: 'notChanged', status: 0 },
+      { id: 3, runId: 1, caseId: 3, editState: 'notChanged', status: 0 },
+      { id: -1, runId: runId, caseId: 4, status: -1, editState: 'new' },
+      { id: -1, runId: runId, caseId: 5, status: -1, editState: 'new' },
+    ]);
+  });
+
+  test('Exclude test cases already included in the test run', () => {
+    const isInclude = false;
+    const keys: number[] = [1, 3];
+    const runId = 1;
+    const currentRunCases = [...initialRuncases];
+    const newRunCases = processRunCases(isInclude, keys, runId, currentRunCases);
+
+    expect(newRunCases).toStrictEqual([
+      { id: 1, runId: 1, caseId: 1, editState: 'deleted', status: 0 },
+      { id: 2, runId: 1, caseId: 2, editState: 'notChanged', status: 0 },
+      { id: 3, runId: 1, caseId: 3, editState: 'deleted', status: 0 },
+    ]);
+  });
+});
diff --git a/frontend/src/app/[locale]/projects/[projectId]/runs/runsControl.ts b/frontend/src/app/[locale]/projects/[projectId]/runs/runsControl.ts
index 857ce94..96723c4 100644
--- a/frontend/src/app/[locale]/projects/[projectId]/runs/runsControl.ts
+++ b/frontend/src/app/[locale]/projects/[projectId]/runs/runsControl.ts
@@ -150,6 +150,55 @@ async function fetchRunCases(jwt: string, runId: number) {
   }
 }
 
+function processRunCases(
+  isInclude: boolean,
+  keys: number[],
+  runId: number,
+  currentRunCases: RunCaseType[]
+): RunCaseType[] {
+  if (isInclude) {
+    const updatedRunCases = currentRunCases.map((runCase) => {
+      if (keys.includes(runCase.caseId) && runCase.editState === 'deleted') {
+        return { ...runCase, editState: 'changed' } as RunCaseType;
+      }
+      return runCase;
+    });
+
+    keys.forEach((caseId) => {
+      const existingRunCase = currentRunCases.find((runCase) => runCase.caseId === caseId);
+      if (!existingRunCase) {
+        updatedRunCases.push({
+          id: -1,
+          runId: runId,
+          caseId: caseId,
+          status: -1,
+          editState: 'new',
+        });
+      }
+    });
+
+    return updatedRunCases;
+  } else {
+    const updatedRunCases = currentRunCases
+      .filter((runCase) => {
+        // If editState is 'new', remove from the array
+        if (keys.includes(runCase.caseId) && runCase.editState === 'new') {
+          return false;
+        }
+        return true;
+      })
+      .map((runCase) => {
+        // If editState isn't 'new', set editState to 'deleted'.
+        if (keys.includes(runCase.caseId) && runCase.editState !== 'new') {
+          return { ...runCase, editState: 'deleted' } as RunCaseType;
+        }
+        return runCase;
+      });
+
+    return updatedRunCases;
+  }
+}
+
 async function updateRunCases(jwt: string, runId: number, runCases: RunCaseType[]) {
   const fetchOptions = {
     method: 'POST',
@@ -175,4 +224,4 @@ async function updateRunCases(jwt: string, runId: number, runCases: RunCaseType[
   }
 }
 
-export { fetchRun, fetchRuns, createRun, updateRun, deleteRun, fetchRunCases, updateRunCases };
+export { fetchRun, fetchRuns, createRun, updateRun, deleteRun, fetchRunCases, processRunCases, updateRunCases };
diff --git a/vitest.config.ts b/vitest.config.ts
index 6143f1e..aa2e9ed 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -7,6 +7,14 @@ export default defineConfig({
       exclude: ['**/node_modules/**', 'docs/**', '**/.next/**'],
       provider: 'v8',
     },
+    exclude: [
+      '**/node_modules/**',
+      '**/dist/**',
+      '**/cypress/**',
+      '**/.{idea,git,cache,output,temp}/**',
+      '**/{karma,rollup,webpack,vite,vitest,jest,ava,babel,nyc,cypress,tsup,build}.config.*',
+      '**/e2e/**',
+    ],
   },
   resolve: {
     alias: [{ find: '@', replacement: resolve(__dirname, './frontend') }],