test: add missing coverage and fix mock return types

Add test for projectDirectoryExists check in custom mode validation
path, which was only covered for full mode. Fix all exec/execFile mock
return values from '' to undefined to match the actual Promise<void>
signatures.

Author: fernandomg

source/__tests__/nonInteractive.test.ts

@@ -114,13 +114,23 @@ describe('nonInteractive — validation', () => {
     expect(output.error).toMatch(/Unknown features: banana/)
   })
 
-  it('rejects when project directory already exists', async () => {
+  it('rejects when project directory already exists (full mode)', async () => {
     vi.mocked(projectDirectoryExists).mockReturnValueOnce(true)
     await expect(runNonInteractive({ name: 'my_app', mode: 'full' })).rejects.toThrow()
     const output = getLastJsonOutput()
     expect(output.success).toBe(false)
     expect(output.error).toMatch(/already exists/)
   })
+
+  it('rejects when project directory already exists (custom mode)', async () => {
+    vi.mocked(projectDirectoryExists).mockReturnValueOnce(true)
+    await expect(
+      runNonInteractive({ name: 'my_app', mode: 'custom', features: 'demo' }),
+    ).rejects.toThrow()
+    const output = getLastJsonOutput()
+    expect(output.success).toBe(false)
+    expect(output.error).toMatch(/already exists/)
+  })
 })
 
 describe('nonInteractive — full mode execution', () => {

source/__tests__/operations/cleanupFiles.test.ts

@@ -2,8 +2,8 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 import type { FeatureName } from '../../constants/config.js'
 
 vi.mock('../../operations/exec.js', () => ({
-  exec: vi.fn().mockResolvedValue(''),
-  execFile: vi.fn().mockResolvedValue(''),
+  exec: vi.fn().mockResolvedValue(undefined),
+  execFile: vi.fn().mockResolvedValue(undefined),
 }))
 
 vi.mock('node:fs', () => ({

source/__tests__/operations/cloneRepo.test.ts

@@ -2,8 +2,8 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { repoUrl } from '../../constants/config.js'
 
 vi.mock('../../operations/exec.js', () => ({
-  exec: vi.fn().mockResolvedValue(''),
-  execFile: vi.fn().mockResolvedValue(''),
+  exec: vi.fn().mockResolvedValue(undefined),
+  execFile: vi.fn().mockResolvedValue(undefined),
 }))
 
 const { exec, execFile } = await import('../../operations/exec.js')
@@ -71,11 +71,9 @@ describe('cloneRepo', () => {
     const callOrder: string[] = []
     vi.mocked(execFile).mockImplementation(async (file, args) => {
       callOrder.push(`${file} ${args[0]}`)
-      return ''
     })
     vi.mocked(exec).mockImplementation(async (_cmd) => {
       callOrder.push('git checkout')
-      return ''
     })
 
     await cloneRepo('my_app')

source/__tests__/operations/installPackages.test.ts

@@ -2,8 +2,8 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { featureDefinitions } from '../../constants/config.js'
 
 vi.mock('../../operations/exec.js', () => ({
-  exec: vi.fn().mockResolvedValue(''),
-  execFile: vi.fn().mockResolvedValue(''),
+  exec: vi.fn().mockResolvedValue(undefined),
+  execFile: vi.fn().mockResolvedValue(undefined),
 }))
 
 const { execFile } = await import('../../operations/exec.js')
@@ -72,7 +72,6 @@ describe('installPackages', () => {
         if (args[0] === 'run' && args[1] === 'postinstall') {
           callOrder.push('postinstall')
         }
-        return ''
       })
 
       await installPackages('/project/my_app', 'custom', ['demo'])