fix: abort process when encountering unrecoverable error (#33)

When encountering an unrecoverable error, the plugin will
fail and exit with code 1 which should stop pipelines.

Unrecoverable errors are:
- merges into the same branch if not allowed
- errors during backmerge

jest.config.js

@@ -6,6 +6,7 @@ module.exports = {
       tsconfig: 'tsconfig.json'
     }
   },
+  clearMocks: true,
   moduleFileExtensions: [
     'js',
     'json',

src/perform-backmerge.ts

@@ -44,7 +44,9 @@ async function performBackmergeIntoBranch(git: Git, pluginConfig: Partial<Config
                         context.logger.error(file)
                     } 
                 }
-                return
+                throw new Error(
+                    'Unable to rebase branch (see error output above).'
+                );
             }
         }
     } else {
@@ -122,6 +124,7 @@ export async function performBackmerge(git: Git, pluginConfig: Partial<Config>,
         } catch (e) {
             context.logger.error('Process aborted due to an error while backmerging a branch.')
             context.logger.error(e)
+            process.exit(1)
             break
         }
     }

test/perform-backmerge.test.ts

@@ -8,6 +8,10 @@ class NullLogger {
     error(message) {}
 }
 
+const realProcessExit = process.exit;
+process.exit = jest.fn(() => "" as never);
+afterAll(() => { process.exit = realProcessExit; });
+
 describe("perform-backmerge", () => {
     jest.mock('semantic-release/lib/get-git-auth-url', () => jest.fn((c) => c.options.repositoryUrl));
 
@@ -438,6 +442,7 @@ describe("perform-backmerge to multiple branches", () => {
         verify(mockedLogger.error('Process aborted due to an error while backmerging a branch.')).once();
         verify(mockedLogger.error(anyString())).once();
         verify(mockedLogger.log('Performing back-merge into develop branch "develop".')).never();
+        expect(process.exit).toBeCalledWith(1);
     });
 
     it("skip conditional backmerge if the release branch does not match the 'from' branch", (done) => {
@@ -548,6 +553,7 @@ describe("perform-backmerge with error", () => {
                 verify(mockedLogger.error('1 modified file(s):')).once();
                 verify(mockedLogger.error('M testfile')).once();
                 verify(mockedGit.push('my-repo', 'develop', false)).never();
+                expect(process.exit).toBeCalledWith(1);
                 done();
             })
             .catch((error) => done(error));