avoid throwing for flow control

src/cli/assert_node_engine_version.ts

@@ -13,13 +13,13 @@ const readActualPackageJSON: () => PackageJSON = () =>
       .toString()
   )
 
-export function assertNodeEngineVersion(
+export function validateNodeEngineVersion(
   currentVersion: string,
   readPackageJSON: () => PackageJSON = readActualPackageJSON
-): void {
+): string {
   const requiredVersion = readPackageJSON().engines.node
   if (!semver.satisfies(currentVersion, requiredVersion)) {
-    const message = `Cucumber can only run on Node.js versions ${requiredVersion}. This Node.js version is ${currentVersion}`
-    throw new Error(message)
+    return `Cucumber can only run on Node.js versions ${requiredVersion}. This Node.js version is ${currentVersion}`
   }
+  return null
 }

src/cli/assert_node_engine_version_spec.ts

@@ -1,18 +1,33 @@
 import assert from 'assert'
-import { assertNodeEngineVersion } from './assert_node_engine_version'
+import { expect } from 'chai'
+import { validateNodeEngineVersion } from './assert_node_engine_version'
 
-describe(assertNodeEngineVersion.name, () => {
-  it('fails when the version is lower than specified in package.json', () => {
-    assert.throws(() =>
-      assertNodeEngineVersion('v11.0.0', () => ({
-        engines: {
-          node: '>=12',
-        },
-      }))
-    )
+describe(validateNodeEngineVersion.name, () => {
+  it('returns an error message when the version is lower than specified in package.json', () => {
+    // Arrange
+
+    // Act
+    const error = validateNodeEngineVersion('v11.0.0', () => ({
+      engines: {
+        node: '>=12',
+      },
+    }))
+
+    // Assert
+    expect(error).to.eql("Cucumber can only run on Node.js versions >=12. This Node.js version is 11.0.0")
   })
 
-  it('passes when the version is greater than specified in package.json', () => {
-    assertNodeEngineVersion('v17.0.0')
+  it('returns null when the version is greater than specified in package.json', () => {
+    // Arrange
+
+    // Act
+    const result = validateNodeEngineVersion('v17.0.0', () => ({
+      engines: {
+        node: '>=12',
+      },
+    }))
+
+    // Assert
+    expect(result).to.eql(null)
   })
 })

src/cli/run.ts

@@ -1,7 +1,7 @@
 import Cli, { ICliRunResult } from './'
 import VError from 'verror'
 import publishBanner from './publish_banner'
-import { assertNodeEngineVersion } from './assert_node_engine_version'
+import { validateNodeEngineVersion } from './assert_node_engine_version'
 
 function exitWithError(error: Error): void {
   console.error(VError.fullStack(error)) // eslint-disable-line no-console
@@ -13,10 +13,9 @@ function displayPublishAdvertisementBanner(): void {
 }
 
 export default async function run(): Promise<void> {
-  try {
-    assertNodeEngineVersion(process.version)
-  } catch (error) {
-    console.error(error.message) // eslint-disable-line no-console
+  const error = validateNodeEngineVersion(process.version)
+  if (error != null) {
+    console.error(error) // eslint-disable-line no-console
     process.exit(1)
   }