diff --git a/src/__tests__/calculate-values.spec.ts b/src/__tests__/calculate-values.spec.ts
new file mode 100644
index 0000000..0ba6d1c
--- /dev/null
+++ b/src/__tests__/calculate-values.spec.ts
@@ -0,0 +1,45 @@
+import calculateValues from '../calculate-values';
+
+jest.mock('node:fs/promises', () => {
+  return {
+    readFile: (fileName: string) => {
+      const mocks: Record<string, string> = {
+        'hello.js': 'alert(42);\n\nconst str = "hello";',
+        '42.ts': 'const str = "hello ts";\nconst n: number = 1;\nconst a: number = n;',
+        'component.tsx': 'const App = () => <div>Hello 1</div>',
+        'legacy.jsx': 'const Legacy = () => <span>Hello 2</span>',
+      };
+      return Promise.resolve(mocks[fileName]);
+    },
+  };
+});
+
+describe('Calculate values', () => {
+  test(`works when ignoreEmptyLines: false`, async () => {
+    const result = await calculateValues(
+      ['hello.js', 'component.tsx', '42.ts', 'legacy.jsx'],
+      false,
+      ['.ts', '.tsx'],
+    );
+
+    expect(result).toEqual({
+      migratedPercentage: 50,
+      totalFilesAll: 4,
+      totalLinesAll: 8,
+      totalFilesTS: 2,
+      totalLinesTS: 4,
+    });
+  });
+
+  test(`works when ignoreEmptyLines: true`, async () => {
+    const result = await calculateValues(['hello.js', '42.ts'], true, ['.ts']);
+
+    expect(result).toEqual({
+      migratedPercentage: 60,
+      totalFilesAll: 2,
+      totalLinesAll: 5,
+      totalFilesTS: 1,
+      totalLinesTS: 3,
+    });
+  });
+});
diff --git a/src/__tests__/e2e.spec.ts b/src/__tests__/e2e.spec.ts
new file mode 100644
index 0000000..54b2604
--- /dev/null
+++ b/src/__tests__/e2e.spec.ts
@@ -0,0 +1,42 @@
+import { exec } from 'node:child_process';
+import util from 'node:util';
+
+const execAsync = util.promisify(exec);
+const testTimeoutMs = 30000;
+
+const stripFormatting = (str: string) => {
+  return (
+    str
+      // Remove bold and reset
+      .replace(/\x1b\[1m/g, '')
+      .replace(/\x1b\[22m/g, '')
+      // Remove underline and reset
+      .replace(/\x1b\[4m/g, '')
+      .replace(/\x1b\[24m/g, '')
+  );
+};
+
+describe('E2E Test on src code', () => {
+  test(
+    'should work with no config and give correct output',
+    async () => {
+      const { stdout: rawStdout, stderr: rawStderr } = await execAsync('pnpm e2e');
+
+      const stdout = stripFormatting(rawStdout);
+      const stderr = stripFormatting(rawStderr);
+
+      expect(stderr).toContain('created dist/es, dist/executable.js');
+      expect(stderr).toContain(`Couldn't find type-coverage.config.json file, using defaults`);
+
+      expect(stdout).toContain('Including files from: src/**/*.{ts,tsx,js,jsx}');
+      expect(stdout).toContain('Excluding files from: **/__tests__/**');
+      expect(stdout).toContain(
+        'The state of the TypeScript migration: we are currently at 100.00%',
+      );
+
+      expect(stdout).toContain('Total Typescript files: 4 (.ts,.tsx)');
+      expect(stdout).toContain('Total files found: 4 (all types)');
+    },
+    testTimeoutMs,
+  );
+});
diff --git a/src/__tests__/normalize-config.spec.ts b/src/__tests__/normalize-config.spec.ts
new file mode 100644
index 0000000..f39688a
--- /dev/null
+++ b/src/__tests__/normalize-config.spec.ts
@@ -0,0 +1,36 @@
+import normalizeConfig, { defaultSettings } from '../normalize-config';
+
+describe('Handle incorrect values', () => {
+  [null, undefined, '', 'hello', true, false].forEach(value => {
+    test(`returns default settings when ${value} used as an input`, () => {
+      expect(normalizeConfig(value as any)).toEqual(defaultSettings);
+    });
+  });
+});
+
+describe('Handle correct values', () => {
+  test(`combines default settings with user override for include`, () => {
+    expect(normalizeConfig('{ "include": "src/**/*.*" }')).toEqual({
+      ...defaultSettings,
+      include: 'src/**/*.*',
+    });
+  });
+  test(`combines default settings with user override for exclude`, () => {
+    expect(normalizeConfig('{ "exclude": ["**/mocks/**", "**/*.cy.{js,jsx,ts,tsx}"] }')).toEqual({
+      ...defaultSettings,
+      exclude: ['**/mocks/**', '**/*.cy.{js,jsx,ts,tsx}'],
+    });
+  });
+  test(`combines default settings with user override for ignoreEmptyLines`, () => {
+    expect(normalizeConfig('{ "ignoreEmptyLines": false }')).toEqual({
+      ...defaultSettings,
+      ignoreEmptyLines: false,
+    });
+  });
+  test(`combines default settings with user override for tsExtensions`, () => {
+    expect(normalizeConfig('{ "tsExtensions": [".ts", ".tsx", ".mts", ".cts"] }')).toEqual({
+      ...defaultSettings,
+      tsExtensions: ['.ts', '.tsx', '.mts', '.cts'],
+    });
+  });
+});