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Assertions let you validate HTTP responses — status codes, response bodies, headers, and latency. They use a fluent API that reads naturally: 
Assert(state["my-request"].status).equals(200)
Assert(state["my-request"].body["name"]).not.isEmpty()

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Assertion subjects

You can assert on four properties of any HTTP request node:

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Status code

Assert(state["req"].status).equals(200)
Assert(state["req"].status).greaterThanOrEqual(200)
Assert(state["req"].status).lessThan(300)

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Response body

Access nested properties with bracket notation. Use .at(index) for array elements: 
// Simple property
Assert(state["req"].body["message"]).equals("ok")

// Nested property
Assert(state["req"].body["data"]["user"]["name"]).equals("Alice")

// Array element
Assert(state["req"].body["items"].at(0)["id"]).isDefined()

// Check the whole body
Assert(state["req"].body["data"]).not.isEmpty()

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Headers

Assert(state["req"].headers["content-type"]).contains("application/json")
Assert(state["req"].headers["x-request-id"]).isDefined()

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Latency

Latency is measured in milliseconds: 
Assert(state["req"].latency).lessThan(2000)
Assert(state["req"].latency).lessThanOrEqual(500)

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Predicates

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Comparison

MethodDescription
.equals(value)Exact equality
.greaterThan(n)Greater than
.lessThan(n)Less than
.greaterThanOrEqual(n)Greater than or equal
.lessThanOrEqual(n)Less than or equal

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String

MethodDescription
.contains(str)Contains substring
.startsWith(str)Starts with prefix
.endsWith(str)Ends with suffix

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Existence

MethodDescription
.isNull()Value is null
.isDefined()Value is not null
.isEmpty()Value is empty (empty string, array, or object)
.isTrue()Value is true
.isFalse()Value is false

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Negation

Prefix any predicate with .not to negate it: 
Assert(state["req"].body["error"]).not.isDefined()
Assert(state["req"].status).not.equals(500)
Assert(state["req"].body["name"]).not.isEmpty()
Assert(state["req"].body["items"]).not.isNull()

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Using with the sequential builder

The sequential builder provides a callback with a type-safe state proxy: 
builder
  .request("users", { ... })
  .assert((state) => [
    Assert(state["users"].status).equals(200),
    Assert(state["users"].body["count"]).greaterThan(0),
  ])
The state proxy only exposes nodes that have been defined above the assertion, giving you compile-time autocomplete.

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Using with the graph builder

With the graph builder, create a state proxy manually using createStateProxy: 
import { createStateProxy, Assert, Assertion } from "@griffin-app/griffin";

const state = createStateProxy(["get-users", "create-user"]);

builder.addNode("validate", Assertion([
  Assert(state["get-users"].status).equals(200),
  Assert(state["create-user"].status).equals(201),
]))

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Multiple assertions

You can add multiple assertion nodes to validate different parts of your flow: 
builder
  .request("create", { ... })
  .assert((state) => [
    Assert(state["create"].status).equals(201),
  ])
  .request("read", { ... })
  .assert((state) => [
    Assert(state["read"].status).equals(200),
    Assert(state["read"].body["name"]).equals("Test"),
  ])
A monitor run is marked as failed if any assertion in any assertion node fails.