# Topics: `Given input topic` / `Given output topic`

> Declare input and output Kafka topics for your scenario.

Source: https://docs.ktestify.xyz/docs/write-tests/background/topics

Topics are the entry points for producers (`input`) and consumers (`output`). You must declare a topic before referencing it in `When` or `Then` steps.

---

## Given input topic

Declares one or more Kafka topics that your test will **produce messages to**.

```gherkin
Given input topic
  | topicName   | topicAlias  | namespace | namespaceAlias |
  | orders-in   | orders-in   |           |                |
```

| Column | Type | Required | Description |
|---|---|---|---|
| `topicName` | `string` | ✅ | Physical Kafka topic name (namespace prefixed automatically) |
| `topicAlias` | `string` | ✅ | Short name used in `When` steps |
| `namespace` | `string` | ❌ | Override namespace for this topic |
| `namespaceAlias` | `string` | ❌ | Reference a named namespace declared in `Given namespaces` |

---

## Given output topic

Declares one or more Kafka topics that your test will **consume and assert messages from**.

```gherkin
Given output topic
  | topicName   | topicAlias  | namespace | namespaceAlias |
  | orders-out  | enriched    | myapp     |                |
```

| Column | Type | Required | Description |
|---|---|---|---|
| `topicName` | `string` | ✅ | Physical Kafka topic name (namespace prefixed automatically) |
| `topicAlias` | `string` | ✅ | Short name used in `Then` steps |
| `namespace` | `string` | ❌ | Override namespace for this topic |
| `namespaceAlias` | `string` | ❌ | Reference a named namespace declared in `Given namespaces` |

:::warning[Input ≠ Output]
KTestify enforces topic type at the context level. Passing an **INPUT** topic to a `Then` step throws a `ConsumerException` immediately. This prevents accidental off-by-one topic confusion.
:::

---

## Multiple topics in one declaration

You can declare multiple topics in one step by adding extra DataTable rows:

```gherkin
Given output topic
  | topicName   | topicAlias |
  | orders-out  | orders     |
  | audit-out   | audit      |
```

---

## Typical background

```gherkin
Background:
  Given namespace
    | namespace |
    | myapp     |
  Given input topic
    | topicName | topicAlias |
    | orders-in | orders-in  |
  Given output topic
    | topicName  | topicAlias |
    | orders-out | orders-out |
```