[wip] Use packageJson key for deepMerge or function

lib/dependency-manager-adapters/base.js

@@ -9,6 +9,27 @@ const Backup = require('../utils/backup');
 const { warn } = require('../utils/console');
 const { LOCKFILE, PACKAGE_JSON } = require('../utils/package-managers');
 
+function merge(a, b) {
+  const copy = {...a};
+
+  for (const k in b) {
+    // for merging arrays, provide your own function
+    if (Array.isArray(k)) {
+      copy[k] = b[k];
+    }
+
+    else if (typeof b[k] === 'object') {
+      copy[k] = merge(a[k] ?? {}, b[k]);
+    }
+
+    else {
+      copy[k] = b[k];
+    }
+  }
+
+  return copy;
+}
+
 class BaseAdapter {
   configKey = 'npm';
   defaultInstallOptions = [];
@@ -41,13 +62,37 @@ class BaseAdapter {
     await this.backup.addFiles([PACKAGE_JSON, this.lockfile]);
   }
 
-  async changeToDependencySet(dependencySet) {
-    await this.applyDependencySet(dependencySet);
-    await this._install(dependencySet);
+  async changePackage(packageJson) {
+    // packageJson can be a function
+    // this.debug('Change package with: %s', JSON.stringify(packageJson));
+
+    const oldPackageJSON = JSON.parse(fs.readFileSync(this.backup.pathForFile(PACKAGE_JSON)));
+    const newPackageJSON = this._applyPackageChanges(oldPackageJSON, packageJson);
 
+    this.debug('Write package.json with: \n', JSON.stringify(newPackageJSON));
+
+    fs.writeFileSync(path.join(this.cwd, PACKAGE_JSON), JSON.stringify(newPackageJSON, null, 2));
+
+    // find the delta of deps
+    // put in the delta here
+    await this._install({});
+
+    // ... and here
+    return this._findChangedDependencies(newPackageJSON);
+  }
+
+  _applyPackageChanges(originalPackage, packageChanges) {
+    if (typeof packageChanges === 'function') {
+      return packageChanges(originalPackage);
+    }
+
+    return merge(originalPackage, packageChanges);
+  }
+
+  async _findChangedDependencies(packageJson) {
     const dependencies = {
-      ...dependencySet.dependencies,
-      ...dependencySet.devDependencies,
+      ...packageJson.dependencies,
+      ...packageJson.devDependencies,
     };
 
     const currentDependencies = Object.keys(dependencies).map((name) => ({
@@ -58,8 +103,13 @@ class BaseAdapter {
     }));
 
     this.debug('Switched to dependencies: \n', currentDependencies);
+  }
+
+  async changeToDependencySet(dependencySet) {
+    await this.applyDependencySet(dependencySet);
+    await this._install(dependencySet);
 
-    return currentDependencies;
+    return this._findChangedDependencies(dependencySet);
   }
 
   async applyDependencySet(dependencySet) {

lib/utils/scenario-manager.js

@@ -15,6 +15,13 @@ module.exports = class ScenarioManager {
     let results = [];
 
     for (let depManager of this.dependencyManagerAdapters) {
+      if ('packageJson' in scenario) {
+        let depManagerResults = await depManager.changePackage(
+          scenario.packageJson
+        );
+        results.push(...depManagerResults);
+      }
+
       if (scenario[depManager.configKey]) {
         let depManagerResults = await depManager.changeToDependencySet(
           scenario[depManager.configKey],