Advanced Assertions

In REST Assured, advanced assertions help you validate complex responses in a more detailed and flexible way. You can check not only basic things like status codes but also deeply nested fields, lists, dynamic values, and more.

In this tutorial, you will learn:

Using Hamcrest Matchers for advanced validations.
Asserting complex JSON responses (arrays, nested objects).
Asserting XML responses with XPath-like checks.
Validating dynamic values and patterns (like regular expressions)
Combining multiple assertions for stronger tests.

Using Hamcrest Matchers for Advanced Assertions

REST Assured uses Hamcrest matchers to write flexible and readable assertions.

Matcher	Description
equalTo(value)	Exact match.
not(equalTo(value))	Opposite of equalTo().
containsString(value)	Partial match for substrings.
startsWith(value)	Checks if the value starts with a prefix.
endsWith(value)	Checks if the value ends with a suffix.
hasItem(item)	Checks if a list contains a value.
hasItems(item1, item2)	Checks if a list contains multiple values.
hasSize(n)	Checks the size of a list or array.
everyItem(condition)	Validates all elements in a list.
greaterThan(value)	Checks if a number is greater.
lessThan(value)	Checks if a number is smaller.
notNullValue()	Ensures the value is not null.

Example 1: Validate Multiple Fields

Java

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/books/20250401")
    .then()
    .body("name", equalTo("Book 1"))
    .body("language", notNullValue())
    .body("publisher", containsString("ABC"));

Example 2: Validate Lists in JSON

Java

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/books")
    .then()
    .body("name", hasItem("Book 1"))         // Check if list contains item
    .body("size()", greaterThan(5));                // Ensure list has more than 5 items

Advanced JSON Assertions

Modern APIs often return complex JSON with arrays and nested objects. REST Assured makes it easy to validate them.

Sample JSON Response:

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{
  "id": 1,
  "name": "Leanne Graham",
  "address": {
    "city": "Gwenborough",
    "zipcode": "92998-3874"
  },
  "phoneNumbers": ["123-456-7890", "987-654-3210"]
}

Validate Nested JSON Fields

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/users/1")
    .then()
    .body("address.city", equalTo("Gwenborough"))
    .body("address.zipcode", startsWith("92998"));

Validate JSON Arrays

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/users/1")
    .then()
    .body("phoneNumbers", hasSize(2))          // Array has 2 items
    .body("phoneNumbers", hasItem("123-456-7890"));

Validate Every Item in an Array

Check if all items in an array meet a condition.

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/users")
    .then()
    .body("address.zipcode", everyItem(startsWith("9")));

Advanced XML Assertions

If the API returns XML, REST Assured allows you to perform advanced checks using XmlPath.

Sample XML Response:

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<user>
    <id>1</id>
    <name>John Doe</name>
    <address>
        <city>New York</city>
    </address>
</user>

Validate XML Elements

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given()
    .accept("application/xml")
    .when()
    .get("http://192.xxx.xx.xxx:8080/users/1")
    .then()
    .body("user.name", equalTo("John Doe"))
    .body("user.address.city", equalTo("New York"));

Validating Dynamic Values

Sometimes API responses contain dynamic values (e.g., timestamps, IDs).

Ignore Dynamic Fields

You can ignore fields that change.

Java

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/books/20250401")
    .then()
    .body("isbn", notNullValue())  // ISBN can be dynamic but not null
    .body("price", greaterThan(0));

Use Regular Expressions

Use matchesPattern() for complex string matching.

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/books/20250401")
    .then()
    .body("createdAt", matchesPattern("\\d{4}-\\d{2}-\\d{2}"));

This checks if createdAt is in YYYY-MM-DD format.

Combining Multiple Assertions

You can combine many checks in a single request.

Complex Assertions

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/users/1")
    .then()
    .statusCode(200)
    .body("name", equalTo("Leanne Graham"))
    .body("address.city", equalTo("Gwenborough"))
    .body("phoneNumbers", hasItem("123-456-7890"))
    .body("phoneNumbers", hasSize(2))
    .header("Content-Type", containsString("json"));

Assert Response Time

You can check if the API responds within a specific time.

Java

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given()
    .when()
    .get("http://192.xxx.xx.xxx:8080/books")
    .then()
    .time(lessThan(2000L));  // Response time < 2 seconds