About this block

Test Mode Fixtures makes the sandbox the pitch. The left column carries the heading, a lede explaining that a test key keeps everything inside the sandbox, three proof points about webhooks, data resets, and free keys, and the two environment keys side by side with Sandbox and Production badges. The right column is a panel of magic recipient addresses, each one deterministically reproducing a failure mode, delivered, bounce, deferred, complaint, and timeout, colored by a status dot.

A proofs array, a keys array, and a fixtures array drive the block, and the fixture rows are the argument, a failure you can trigger on demand is a failure you can test.

When to use

Reach for this block on developer pages where testability is the selling point, teams that have been burned by sandboxes that only ever return success. It reads best after the reader has seen the API work once and is now asking how to prove their own error handling before going live.

A natural flow around it on a Marketing Pro page:

Before

• SDK grid proving the language coverage before the testing story

After

• Error codes the fixtures are designed to reproduce
• CTA with the free sandbox key signup

What you can display

One strong use is your real magic recipient list with honest outcomes. Other panels:

• Seed presets. Named datasets a sandbox can load on request.
• Simulated states. Cards or accounts that force each edge.
• Test card numbers. The classic decline and success set.

Tip: name the ugly outcomes, a bounce and a spam complaint in the list say the sandbox was built by people who ship.