Java Programming Tutorials

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JUnit Assert CheatSheet

JUnit Assert is the most fundamental class in JUnit. In this post we’re going to show what are its abilities and how to use it correctly. Read on!

JUnit Assert CheatSheet

The following test shows how static helper methods from org.junit.Assert can be used to verify state of objects under the test:

package com.farenda.junit;

import org.junit.Test;

import static java.util.Collections.emptyList;
import static org.junit.Assert.*;

public class AssertionsTest {

    @Test
    public void shouldAssertEqualElements() {
        assertEquals(3, 3); // integers
        assertEquals(3.14, 3.14, 0.0001); // compare doubles with delta!
        assertEquals("Java", "Java"); // objects
        assertEquals("The descriptive message!", 3, 3); // with message
    }

    @Test
    public void shouldAssertArrayEquality() {
        assertArrayEquals(new int[]{1, 2, 3}, new int[]{1, 2, 3});
        assertArrayEquals("Those tables!",
                new boolean[]{true}, new boolean[]{true});
    }

    @Test
    public void shouldShowInequality() {
        assertNotEquals(3, 2+2);
        assertNotEquals("Close, but no.", 3.14, 3.1415, 0.0001);
    }

    @Test
    public void shouldAssertBooleanResults() {
        assertTrue(emptyList().isEmpty());
        assertTrue("It should be empty", emptyList().isEmpty());

        assertFalse("Yoda".isEmpty());
        assertFalse("There should be only one!", "Yoda".isEmpty());
    }

    @Test
    public void shouldTestNullness() {
        assertNull(null);
        assertNull("This one have to be null", null);

        assertNotNull("Han Solo");
        assertNotNull("Should not happen!", new Object());
    }

    @Test
    public void shouldFindTheSameObject() {
        String jedi = "Luke S";
        assertSame("There's only one Jedi!", jedi, jedi);
        assertNotSame("These guys are different!", new Object(), new Object());
    }
}

Important thing to note is that double and float numbers have to be compared with some accuracy, due to limitations of computers to represent numbers. In our case accuracy of 0.00001 is more than enough.

How pros do it

As in the previous post we’ll take one example from Facebook Fresco:

package com.facebook.common.util;

import org.junit.Test;

import static org.junit.Assert.*;

/** Unit test for {@link TriState}. */
public class TriStateTest {

  @Test
  public void testValueOf() {
    assertEquals(TriState.YES, TriState.valueOf(true));
    assertEquals(TriState.NO, TriState.valueOf(false));
  }

  // ...

  @Test
  public void testAsBooleanValidValues() {
    assertTrue(TriState.YES.asBoolean());
    assertFalse(TriState.NO.asBoolean());
  }

  // ...

  @Test
  public void testAsBooleanObject() {
    assertSame(Boolean.TRUE, TriState.YES.asBooleanObject());
    assertSame(Boolean.FALSE, TriState.NO.asBooleanObject());
    assertNull(TriState.UNSET.asBooleanObject());
  }
}

Another one from Spring Framework Base64UtilsTests:

package org.springframework.util;

import org.junit.Test;

import static org.junit.Assert.*;

/**
 * @author Juergen Hoeller
 * @since 4.2
 */
public class Base64UtilsTests {

        // ... other tests removed for brevity

        @Test
        public void encodeDecodeUrlSafe() {
                byte[] bytes = new byte[] { (byte) 0xfb, (byte) 0xf0 };
                assertArrayEquals("-_A=".getBytes(), Base64Utils.encodeUrlSafe(bytes));
                assertArrayEquals(bytes, Base64Utils.decodeUrlSafe(Base64Utils.encodeUrlSafe(bytes)));

                assertEquals("-_A=", Base64Utils.encodeToUrlSafeString(bytes));
                assertArrayEquals(bytes, Base64Utils.decodeFromUrlSafeString(Base64Utils.encodeToUrlSafeString(bytes)));
        }
}

Happy testing! :-)

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