hardening and bugfixing prior to stable release

packages/nopy/tests/errors.test.ts

@@ -0,0 +1,62 @@
+/**
+ * Tests for nopy.errors — how a failed run is presented.
+ */
+
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { NopyUsageError, reportError } from '../src/nopy.errors.js';
+
+let out: ReturnType<typeof vi.spyOn>;
+let err: ReturnType<typeof vi.spyOn>;
+
+/** Everything written to stderr by the last call, as one string. */
+const stderr = () => err.mock.calls.map((call) => String(call[0])).join('\n');
+
+beforeEach(() => {
+  out = vi.spyOn(console, 'log').mockImplementation(() => {});
+  err = vi.spyOn(console, 'error').mockImplementation(() => {});
+  delete process.env.NOPY_DEBUG;
+});
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+describe('reportError', () => {
+  it('prints a usage error as one line and points at the debug switch', () => {
+    reportError(new NopyUsageError('No .nopyrc.json found'));
+
+    expect(stderr()).toContain('Error: No .nopyrc.json found');
+    expect(stderr()).not.toContain('nopy.errors');
+    expect(stderr()).toContain('NOPY_DEBUG=1');
+  });
+
+  it('keeps the stack for anything unexpected', () => {
+    reportError(new TypeError('cannot read properties of undefined'));
+
+    expect(stderr()).toContain('Error: cannot read properties of undefined');
+    expect(stderr()).toContain('TypeError: cannot read properties of undefined\n    at ');
+    expect(stderr()).not.toContain('NOPY_DEBUG=1');
+  });
+
+  it('prints the stack of a usage error under NOPY_DEBUG', () => {
+    process.env.NOPY_DEBUG = '1';
+
+    reportError(new NopyUsageError('No .nopyrc.json found'));
+
+    expect(stderr()).toContain('NopyUsageError: No .nopyrc.json found\n    at ');
+    expect(stderr()).not.toContain('NOPY_DEBUG=1 for');
+  });
+
+  it('reports a thrown non-error', () => {
+    reportError('just a string');
+
+    expect(stderr()).toContain('Error: just a string');
+    expect(stderr()).toContain('NOPY_DEBUG=1');
+  });
+
+  it('says nothing on stdout', () => {
+    reportError(new NopyUsageError('No .nopyrc.json found'));
+
+    expect(out).not.toHaveBeenCalled();
+  });
+});