test: add test case for downloadWithBackup()

ts-binary-wrapper/test/unit/common.spec.ts

@@ -250,6 +250,47 @@ describe('Testing binary bootstrapper', () => {
     fs.unlinkSync(shasumFile);
     fs.unlinkSync(config.getLocalLocation());
   });
+  it('downloadWithBackup() succesfull', async () => {
+    const binaryName = 'snyk-macos';
+    const shafileExtension = '.sha256';
+    const config = new common.WrapperConfiguration('1.1080.0', binaryName, '');
+    const shasumFile =
+      config.getLocalLocation() + Math.random() + shafileExtension;
+
+    // download the shasum first, here we don't expect a shasum comparison
+    const shasumDownload = await common.downloadWithBackup(
+      'https://notdownloads.snyk.io/cli/v1.1080.0/snyk-macos.sha256',
+      config.getDownloadLocation() + shafileExtension,
+      shasumFile,
+      '',
+    );
+    expect(shasumDownload).toBeUndefined();
+    expect(fs.existsSync(shasumFile)).toBeTruthy();
+    const expectedShasum = common.getCurrentSha256sum(binaryName, shasumFile);
+
+    // download binary next and use previously downloaded shasum to check validity
+    const binaryDownload = await common.downloadExecutable(
+      config.getDownloadLocation(),
+      config.getLocalLocation(),
+      expectedShasum,
+    );
+    expect(binaryDownload).toBeUndefined();
+    expect(fs.existsSync(config.getLocalLocation())).toBeTruthy();
+
+    const stats = fs.statSync(config.getLocalLocation());
+    expect(stats.mode).toEqual(0o100755);
+
+    try {
+      // check if the binary is executable
+      fs.accessSync(config.getLocalLocation(), fs.constants.X_OK);
+    } catch {
+      // execution of binary not possible
+      expect(false).toBeTruthy();
+    }
+
+    fs.unlinkSync(shasumFile);
+    fs.unlinkSync(config.getLocalLocation());
+  });
 
   it('downloadExecutable() fails due to incorrect shasum', async () => {
     const binaryName = 'snyk-macos';