fix(jsii-diff): renaming a positional argument is a breaking change in Python

Related: #2927

Author: RomainMuller

packages/jsii-diff/test/python.test.ts

@@ -0,0 +1,24 @@
+import { expectError } from './util';
+
+// ----------------------------------------------------------------------
+
+test.each([
+  ['class', 'constructor'],
+  ['class', 'method'],
+  ['interface', 'method'],
+])(
+  'not okay to rename a positional parameter',
+  (scope, decl) =>
+    expectError(
+      /positional parameter was renamed from 'previous' to 'current'/,
+      // Note: name is ITest so we're good for both class & interface... Yes, this is ugly.
+      `
+      export ${scope} ITest {
+        ${decl}(previous: any)${decl === 'constructor' ? '' : ': void'}${scope === 'class' ? ' { previous.use(); }' : ';'}
+      }`,
+      `
+      export ${scope} ITest {
+        ${decl}(current: any)${decl === 'constructor' ? '' : ': void'}${scope === 'class' ? ' { current.use(); }' : ';'}
+      }`,
+    ),
+);