Overwrite process exit call, when needed

This should make testing of the Cli application much easier.

packages/cli/src/CliApplication.ts

@@ -3,6 +3,7 @@ import type {
     OutputConfiguration
 } from "commander";
 import { Command as CommanderJs } from "commander";
+import SkipProcessExitError from "./exceptions/SkipProcessExitError";
 import { version } from "../package.json";
 import * as process from "node:process";
 
@@ -19,6 +20,15 @@ export default class CliApplication
      * @protected
      */
     protected _driver: CommanderJs;
+
+    /**
+     * State whether `process.exit()` is permitted invoked or not.
+     * 
+     * @type {boolean}
+     * 
+     * @protected
+     */
+    protected _allowProcessExit: boolean = true;
 
     // TODO
     constructor()
@@ -69,6 +79,35 @@ export default class CliApplication
 
         return this;
     }
+
+    /**
+     * Specify whether the Cli Application must invoke `process.exit()` or not.
+     * 
+     * **Note**: _Process exit is only prevented, if the `run()`'s [options]{@link import('commander').ParseOptions}
+     * argument is set to `{ from: "user" }`!_
+     * 
+     * @param {boolean} [allow=true]
+     * 
+     * @return {this}
+     */
+    public allowProcessExit(allow: boolean = true): this
+    {
+        this._allowProcessExit = allow;
+
+        return this;
+    }
+
+    /**
+     * Opposite of {@link allowProcessExit}
+     * 
+     * @param {boolean} [prevent=true]
+     * 
+     * @return {this}
+     */ 
+    public preventProcessExit(prevent: boolean = true): this
+    {
+        return this.allowProcessExit(!prevent);
+    }
 
     // TODO:...
     public async run(argv?: readonly string[], options?: ParseOptions)
@@ -77,13 +116,26 @@ export default class CliApplication
 
         // TODO: ... Add commands to the underlying driver.
 
+        // Overwrite process exit, if needed.
+        if (!this._allowProcessExit && options?.from === 'user') {
+            this.overwriteProcessExit();
+        }
+
         // When no arguments are given, then force display the default help.
         if ((argv === undefined && process.argv.length < 3) || argv?.length === 0) {
             driver.help();
         }
 
         // Run the application...
-        await driver.parseAsync(argv, options);
+        try {
+            await driver.parseAsync(argv, options);    
+        } catch (e) {
+            // Re-throw error, if it's not a "skip process exit" error. 
+            if (!(e instanceof SkipProcessExitError)) {
+                throw e;
+            }
+        }
+
 
         return Promise.resolve(this);
     }
@@ -101,4 +153,22 @@ export default class CliApplication
             .version(this.version)
             .description(this.description);
     }
+
+    /**
+     * Overwrites the process exit call, in the "driver"
+     * 
+     * @protected
+     */
+    protected overwriteProcessExit(): void
+    {
+        this.driver.exitOverride((err) => {
+            // When command was successful, wrap the command error into a "skip process exit" error 
+            if (err.exitCode === 0) {
+                throw new SkipProcessExitError(err.message, { cause: { previous: err } })
+            }
+
+            // Otherwise, simply re-throw error
+            throw err;
+        })
+    }
 }