JsonUnit

JsonUnit is a library that simplifies JSON comparison in unit tests. The usage is simple:

import static net.javacrumbs.jsonunit.JsonAssert.*;
import static net.javacrumbs.jsonunit.core.Option.*;

...

// compares two JSON documents
assertJsonEquals("{\"test\":1}", "{\n\"test\": 1\n}");

// objects are automatically serialized before comparison
assertJsonEquals(jsonObject, "{\n\"test\": 1\n}");

// compares only part
assertJsonPartEquals("2", "{\"test\":[{\"value\":1},{\"value\":2}]}",
    "test[1].value");
    
// extra options can be specified
assertJsonEquals("{\"test\":{\"a\":1}}",
    "{\"test\":{\"a\":1, \"b\": null}}",
    when(TREATING_NULL_AS_ABSENT));

// compares only the structure, not the values
assertJsonEquals("[{\"test\":1}, {\"test\":2}]",
    "[{\n\"test\": 1\n}, {\"TEST\": 4}]", when(IGNORING_VALUES))

// Lenient parsing of expected value
assertJsonEquals("{//Look ma, no quotation marks\n test:'value'}", 
    "{\n\"test\": \"value\"\n}");

When the values are compared, order of elements and whitespaces are ignored.

Hamcrests matchers

You use Hamcrest matchers in the following way

import static net.javacrumbs.jsonunit.JsonMatchers.*;
import static org.junit.Assert.*;
import static net.javacrumbs.jsonunit.core.util.ResourceUtils.resource;
...

assertThat("{\"test\":1}", jsonEquals("{\"test\": 1}"));
assertThat("{\"test\":1}", jsonPartEquals("test", 1));
assertThat("{\"test\":[1, 2, 3]}", jsonPartEquals("test[0]", 1));

assertThat("{\"test\":{\"a\":1, \"b\":2, \"c\":3}}",
    jsonEquals("{\"test\":{\"b\":2}}").when(IGNORING_EXTRA_FIELDS));

// Can use other Hamcrest matchers too
assertThat("{\"test\":1}", jsonPartMatches("test", is(valueOf(1))))

assertThat("{\"test\":1}", jsonEquals(resource("test.json")));

Fluent assertions

Fluent (FEST or AssertJ like) assertions are supported by a special module json-unit-fluent

import static net.javacrumbs.jsonunit.fluent.JsonFluentAssert.assertThatJson;
...

// compares entire documents
assertThatJson("{\"test\":1}").isEqualTo("{\"test\":2}");

// compares only parts of the document
assertThatJson("{\"test1\":2, \"test2\":1}")
    .node("test1").isEqualTo(2)
    .node("test2").isEqualTo(2);

// compare node indexed from start of array
assertThatJson("{\"root\":{\"test\":[1,2,3]}}")
    .node("root.test[0]").isEqualTo(1);

// compare node indexed from end of array
assertThatJson("{\"root\":{\"test\":[1,2,3]}}")
    .node("root.test[-1]").isEqualTo(3);

// compares only the structure
assertThatJson("{\"test\":1}")
    // Options have to be specified before the assertion
    .when(IGNORING_VALUES)
    .isEqualTo("{\"test\":21}");

// ignores a value
assertThatJson("{\"test\":1}").isEqualTo("{\"test\":\"${json-unit.ignore}\"}");

// ignores extra fields
assertThatJson("{\"test\":{\"a\":1, \"b\":2, \"c\":3}}")
    // Options have to be specified before the assertion
    .when(IGNORING_EXTRA_FIELDS)
    .isEqualTo("{\"test\":{\"b\":2}}");
    	
// array length comparison
assertThatJson("{\"test\":[1,2,3]}").node("test")
    .isArray().ofLength(2);
    
// array contains node
assertThatJson("{\"test\":[{\"id\":36},{\"id\":37}]}").node("test")
.isArray().thatContains("{\"id\":37}");

// using Hamcrest matcher
assertThatJson("{\"test\":\"one\"}").node("test")
    .matches(equalTo("one"));

import static java.math.BigDecimal.valueOf;
...
// Numbers sent to matchers are BigDecimals.
assertThatJson("{\"test\":[{\"value\":1},{\"value\":2},{\"value\":3}]}")
    .node("test")
    .matches(everyItem(jsonPartMatches("value", lessThanOrEqualTo(valueOf(4)))));

Hamcrest matchers in fluent assertions

It is possible to combine fluent assertions with hamcrest matchers using matches method. For example

assertThatJson("{\"test\":[1,2,3]}").node("test").matches(hasItem(valueOf(1)));

assertThatJson("{\"test\":[{\"value\":1},{\"value\":2},{\"value\":3}]}")
    .node("test")
    .matches(everyItem(jsonPartMatches("value", lessThanOrEqualTo(valueOf(4)))));

Spring MVC assertions

Since version 1.7.0 JsonUnit supports Spring MVC test assertions. For example

import static net.javacrumbs.jsonunit.spring.JsonUnitResultMatchers.json;
...

this.mockMvc.perform(get("/sample").andExpect(
    json().isEqualTo("{\"result\":{\"string\":\"stringValue\", \"array\":[1, 2, 3],\"decimal\":1.00001}}")
);
this.mockMvc.perform(get("/sample").andExpect(
    json().node("result.string2").isAbsent()
);
this.mockMvc.perform(get("/sample").andExpect(
    json().node("result.array").when(Option.IGNORING_ARRAY_ORDER).isEqualTo(new int[]{3, 2, 1})
);
this.mockMvc.perform(get("/sample").andExpect(
    json().node("result.array").matches(everyItem(lessThanOrEqualTo(valueOf(4))))
);

Ignoring values

Sometimes you need to ignore certain values when comparing. It is possible to use ${json-unit.ignore} placeholder like this

assertJsonEquals("{\"test\":\"${json-unit.ignore}\"}",
    "{\n\"test\": {\"object\" : {\"another\" : 1}}}");

Ignoring paths

assertJsonEquals(
     "{\"root\":{\"test\":1, \"ignored\": 2}}", 
     "{\"root\":{\"test\":1, \"ignored\": 1}}", 
     whenIgnoringPaths("root.ignored")
);

Regular expressions

It is also possible to use regular expressions to compare string values

assertJsonEquals("{\"test\": \"${json-unit.regex}[A-Z]+\"}", 
    "{\"test\": \"ABCD\"}");

Type placeholders

If you want to assert just a type, but you do not care about the exact value, you can use any-* placeholder like this

assertThatJson("{\"test\":\"value\"}")
    .isEqualTo("{test:'${json-unit.any-string}'}");

assertThatJson("{\"test\":true}")
    .isEqualTo("{\"test\":\"${json-unit.any-boolean}\"}");
    
assertThatJson("{\"test\":1.1}")
    .isEqualTo("{\"test\":\"${json-unit.any-number}\"}");

Custom matchers

In some special cases you might want to use your own matcher in the expected document.

 assertJsonEquals(
     "{\"test\": \"${json-unit.matches:positive}\"}", 
     "{\"test\":1}", 
     JsonAssert.withMatcher("positive", greaterThan(valueOf(0)))
 );

In even more special cases, you might want to parametrize your matcher.

 Matcher<?> divisionMatcher = new DivisionMatcher();
 assertJsonEquals(
     "{test: '${json-unit.matches:isDivisibleBy}3'}", 
     "{\"test\":5}", 
     JsonAssert.withMatcher("isDivisibleBy", divisionMatcher)
 );
 
 private static class DivisionMatcher extends BaseMatcher<Object> implements ParametrizedMatcher {
     private BigDecimal param;

     public boolean matches(Object item) {
         return ((BigDecimal)item).remainder(param).compareTo(ZERO) == 0;
     }

     public void describeTo(Description description) {
         description.appendValue(param);
     }

     @Override
     public void describeMismatch(Object item, Description description) {
         description.appendText("It is not divisible by ").appendValue(param);
     }

     public void setParameter(String parameter) {
         this.param = new BigDecimal(parameter);
     }
 }

Options

There are multiple options how you can configure the comparison

TREATING_NULL_AS_ABSENT - fields with null values are equivalent to absent fields. For example, this test passes

assertJsonEquals("{\"test\":{\"a\":1}}",
    "{\"test\":{\"a\":1, \"b\": null, \"c\": null}}",
    when(TREATING_NULL_AS_ABSENT));

IGNORING_ARRAY_ORDER - ignores order in arrays

assertJsonEquals("{\"test\":[1,2,3]}", 
    "{\"test\":[3,2,1]}",
    when(IGNORING_ARRAY_ORDER));

IGNORING_EXTRA_ARRAY_ITEMS - ignores unexpected array items

assertJsonEquals("{\"test\":[1,2,3]}",
    "{\"test\":[1,2,3,4]}",
    when(IGNORING_EXTRA_ARRAY_ITEMS));


assertJsonEquals("{\"test\":[1,2,3]}",
    "{\"test\":[5,5,4,4,3,3,2,2,1,1]}",
    when(IGNORING_EXTRA_ARRAY_ITEMS, IGNORING_ARRAY_ORDER));

IGNORING_EXTRA_FIELDS - ignores extra fields in the compared value

assertJsonEquals("{\"test\":{\"b\":2}}", 
    "{\"test\":{\"a\":1, \"b\":2, \"c\":3}}",
    when(IGNORING_EXTRA_FIELDS));

IGNORE_VALUES - ignores values and compares only types

assertJsonEquals("{\"test\":{\"a\":1,\"b\":2,\"c\":3}}", 
    "{\"test\":{\"a\":3,\"b\":2,\"c\":1}}",
    when(IGNORING_VALUES));

It is possible to combine options.

assertJsonEquals("{\"test\":[{\"key\":1},{\"key\":2},{\"key\":3}]}", 
    "{\"test\":[{\"key\":3},{\"key\":2, \"extraField\":2},{\"key\":1}]}",
    when(IGNORING_ARRAY_ORDER, IGNORING_EXTRA_FIELDS));

In Hamcrest assertion you can set the option like this

assertThat("{\"test\":{\"a\":1, \"b\":2, \"c\":3}}",
    jsonEquals("{\"test\":{\"b\":2}}").when(IGNORING_EXTRA_FIELDS));

For standard asserts and Hamcrest matchers, it is possible to set the configuration globally

JsonAssert.setOptions(IGNORING_ARRAY_ORDER, IGNORING_EXTRA_FIELDS);

In fluent assertion, you can set options in the following way

assertThatJson("{\"test\":{\"a\":1, \"b\":2, \"c\":3}}")
    .when(IGNORING_EXTRA_FIELDS).isEqualTo("{\"test\":{\"b\":2}}");

Please note that when method has to be called before the actual comparison.

Numeric comparison

Numbers are by default compared in the following way:

• If the type differs, the number is different. So 1 and 1.0 are different (int vs. float). This does not apply when Moshi is used since it parses all numbers as Doubles.
• Floating number comparison is exact

You can change this behavior by setting tolerance

assertJsonEquals("1", "\n1.009\n", withTolerance(0.01));

or globally

JsonAssert.setTolerance(0.01);

or for fluent assertions

assertThatJson("{\"test\":1.00001}").node("test").withTolerance(0.001).isEqualTo(1);

Or you can use Hamcrest matcher

import static java.math.BigDecimal.valueOf;
...
assertThatJson("{\"test\":1.10001}").node("test")
    .matches(closeTo(valueOf(1.1), valueOf(0.001)));

Logging

Although the differences are printed out by the assert statement, sometimes you use JsonUnit with other libraries like Jadler that do not print the differences between documents. In such case, you can switch on the logging. JsonUnit uses SLF4J. The only thing you need to do is to configure your logging framework to log net.javacrumbs.jsonunit.difference on DEBUG level.

Selecting underlying library

JsonUnit is trying to cleverly match which JSON library to use. In case you need to change the default behavior, you can use json-unit.libraries system property. For example -Djson-unit.libraries=jackson2,gson or System.setProperty("json-unit.libraries", "jackson1");. Supported values are gson, json.org, moshi, jackson1, jackson2

Maven dependency

JsonUnit is accessible in Maven central repository. In order for it to work, you need either, Jackson 1.x, Jackson 2.x, Gson, JSONObject or Moshi on the classpath.

<dependency>
    <groupId>net.javacrumbs.json-unit</groupId>
    <artifactId>json-unit</artifactId>
    <version>1.27.0</version>
    <scope>test</scope>
</dependency>

To use fluent assertions:

<dependency>
    <groupId>net.javacrumbs.json-unit</groupId>
    <artifactId>json-unit-fluent</artifactId>
    <version>1.27.0</version>
    <scope>test</scope>
</dependency>

To use Spring MVC assertions:

<dependency>
    <groupId>net.javacrumbs.json-unit</groupId>
    <artifactId>json-unit-spring</artifactId>
    <version>1.27.0</version>
    <scope>test</scope>
</dependency>

Licence

JsonUnit is licensed under Apache 2.0 licence.

Release notes

1.27.0

• Better array comparison and error messages

1.26.0

• IDE friendly error messages
• isStringEqualTo is chainable (thanks to @gsson)
• Dropped support of Java 5
• Automatic module names added

1.25.1

• Support for Jackson BinaryNode

1.25.0

• Support for ignoring paths whenIgnoringPaths()

1.24.0

• Support for parametrers in custom matchers ${json-unit.matches:matcherName}param

1.23.0

• Support for custom matchers ${json-unit.matches:matcherName}

1.22.0

• Support for Moshi

1.21.0

• Better diff reporting for unordered arrays with single difference

1.20.0

• Negative array indexes added (thanks roxspring)

1.19.0

• isArray().thatContains(...) fluent assert added

1.18.0

• Resource reading helper added

1.17.0

• System property to specify JSON libraries to be used

1.16.1

• Array pattern accepts non-word characters

1.16.0

• isAbsent and isPresent checks take TREAT_NULL_AS_ABSENT into account

1.15.0

• Dependency on slf4j made optional

1.14.1

• Preferring org.json library to process JSONArray

1.14.0

• Support for org.json library
• Fix: Element out of array bounds is treated as missing

1.13.0

• Support for any-* placeholders

1.12.1

• Single quote values in expected String allowed

1.12.0

• Lenient parsing of expected values

1.11.0

• Option setting methods made deprecated if called after assertion in JsonFluentAssert
• JsonFluentAssert constructors made private. Please file an issue if you need them.

1.10.0

• Added support for IGNORING_EXTRA_ARRAY_ITEMS

1.9.0

• Made compatible with Jackson 1.4

1.8.0

• OSGi support thanks to @amergey

1.7.0

• Support for Spring MVC tests assertions

1.6.1

• Gson nodes are not reconverted

1.6.0

• Added support for Hamcrest matchers

1.5.6

• Fixed handling of empty value in the expected parameter

1.5.5

• Support for dot in node name

1.5.4

• Added isObject method to fluent assertions

1.5.3

• Jackson 1 is preferred if the serialized class contains Jackson1 annotation

1.5.2

• Added support for regular expressions

1.5.1

• isStringEqualTo() added to fluent assertions
• isArray added to fluent assertions

1.5.0

• One runtime now supports Jackson 1.x, Jackson 2.x and Gson
• Internal JsonUnit class changed in backwards incompatible way

1.3.0 + 0.3.0

• Options renamed
• assertJsonNot* asserts added
• Support for online configuration in Hamcrest and standard asserts added

1.2.0 + 0.2.0

• Error messages changed a bit when comparing structures
• Refactoring of internal classes
• Support for ignoring array order
• Support for ignoring values
• Support for ignoring extra fields

1.1.6 + 0.1.6

• Treat null as absent added

1.1.5 + 0.1.5

• Absence/presence tests added

1.1.4 + 0.1.4

• Path to array in root fixed

1.1.3 + 0.1.3

• Numeric comparison tolerance added

1.1.2 + 0.1.2

• jsonStringEquals and jsonStringPartEquals added

1.1.1 + 0.1.1

• Generics in JsonMatchers fixed

1.1.0 + 0.1.0

• Simplified API
• Invalid JSONs in String comparison quoted
• Runtime incompatible (compile-time compatible) changes

1.0.0

• Switched to Jackson 2.x
• Fluent JsonAssert renamed to JsonFluentAssert

0.0.16

• Fluent assertions made framework independent.

0.0.15

• Switched from FEST to AssertJ

0.0.14

• Modules refactored
• Added support for FEST assert

0.0.13

• Logging categories changed

0.0.12

• Added logging

0.0.11

• Ignore placeholder "${json-unit.ignore}" added

0.0.10

• Text differences are closed in quotes

0.0.9

• Matchers added

0.0.7

• Made Java 5 compatible

0.0.6

• assertJsonPartStructureEquals added

0.0.5

• assertJsonPartEquals added

0.0.4

• Better error messages in case of different types

0.0.3

• Support for array types and other oddities in root

0.0.2

• Support for nulls