AssertJ for Guava

1. Overview

This article focuses on AssertJ Guava-related assertions and is the second article from the AssertJ series. If you want to some general info about AssertJ, have a look at the first article in the series Introduction to AssertJ.

2. Maven Dependencies

In order to use AssertJ with Guava, you need to add the following dependency to your pom.xml:

<dependency>
    <groupId>org.assertj</groupId>
    <artifactId>assertj-guava</artifactId>
    <version>3.0.0</version>
    <scope>test</scope>
</dependency>

You can find the latest version here.

And note that since version 3.0.0, AssertJ Guava relies on Java 8 and AssertJ Core 3.x.

3. Guava Assertions in Action

AssertJ has custom assertions for Guava types: ByteSource, Multimap, Optional, Range, RangeMap and Table.

3.1. ByteSource Assertions

Let’s start off by creating two empty temporary files:

File temp1 = File.createTempFile("bael", "dung1");
File temp2 = File.createTempFile("bael", "dung2");

and creating ByteSource instances from them:

ByteSource byteSource1 = Files.asByteSource(temp1);
ByteSource byteSource2 = Files.asByteSource(temp2);

Now we can write the following assertion:

assertThat(buteSource1)
  .hasSize(0)
  .hasSameContentAs(byteSource2);

3.2. Multimap Assertions

Multimaps are maps that can associate more than one value with a given key. The Multimap assertions work pretty similarly to normal Map implementations.

Let’s start by creating a Multimap instance and adding some entries:

Multimap<Integer, String> mmap = Multimaps
  .newMultimap(new HashMap<>(), Sets::newHashSet);
mmap.put(1, "one");
mmap.put(1, "1");

And now we can assert:

assertThat(mmap)
  .hasSize(2)
  .containsKeys(1)
  .contains(entry(1, "one"))
  .contains(entry(1, "1"));

There are also two additional assertions available – with subtle difference between them:

• containsAllEntriesOf and
• hasSameEntriesAs.

Let’s have a look at these two assertions; we’ll start by defining a few maps:

Multimap<Integer, String> mmap1 = ArrayListMultimap.create();
mmap1.put(1, "one");
mmap1.put(1, "1");
mmap1.put(2, "two");
mmap1.put(2, "2");

Multimap<Integer, String> mmap1_clone = Multimaps
  .newSetMultimap(new HashMap<>(), HashSet::new);
mmap1_clone.put(1, "one");
mmap1_clone.put(1, "1");
mmap1_clone.put(2, "two");
mmap1_clone.put(2, "2");

Multimap<Integer, String> mmap2 = Multimaps
  .newSetMultimap(new HashMap<>(), HashSet::new);
mmap2.put(1, "one");
mmap2.put(1, "1");

As you can see, mmap1 and mmap1_clone contain exactly the same entries, but are two different objects of two different Map types. The Map mmap2 contains a single entry that is shared among all maps. Now the following assertion is true:

assertThat(mmap1)
  .containsAllEntriesOf(mmap2)
  .containsAllEntriesOf(mmap1_clone)
  .hasSameEntriesAs(mmap1_clone);

3.3. Optional Assertions

Assertions for Guava’s Optional involve value presence checking and utilities for extracting the inner value.

Let’s start by creating an Optional instance:

Optional<String> something = Optional.of("something");

And now we can check the value’s presence and assert the Optional‘s content:

assertThat(something)
  .isPresent()
  .extractingValue()
  .isEqualTo("something");

3.4. Range Assertions

Assertions for Guava’s Range class involves checking Range‘s lower and upper bounds or whether a certain value is within a given range.

Let’s define a simple range of characters by doing the following:

Range<String> range = Range.openClosed("a", "g");

and now we can test:

assertThat(range)
  .hasOpenedLowerBound()
  .isNotEmpty()
  .hasClosedUpperBound()
  .contains("b");

3.5. Table Assertions

AssertJ’s table-specific assertions allow the checking of row and column count and the presence of a cells value.

Let’s create a simple Table instance:

Table<Integer, String, String> table = HashBasedTable.create(2, 2);
table.put(1, "A", "PRESENT");
table.put(1, "B", "ABSENT");

and now we can perform the following check:

assertThat(table)
  .hasRowCount(1)
  .containsValues("ABSENT")
  .containsCell(1, "B", "ABSENT");

4. Conclusion

In this article from AssertJ series, we explored all Guava-related features.

The implementation of all the examples and code snippets can be found in a GitHub project.