How do I test for an exact Exception message, rather than a substring, with PHPUnit?

Question

According to the PHPUnit Documentation on @expectedExceptionMessage, the string must only be a substring of the actual Exception thrown.

In one of my validation methods, an array item is pushed for each error that occurs, and the final Exception message is displayed by imploding the array of errors.

class MyClass
{
    public function validate($a, $b, $c, $d)
    {
        if($a < $b) $errors[] = "a < b.";
        if($b < $c) $errors[] = "b < c.";
        if($c < $d) $errors[] = "c < d.";

        if(count($errors) > 0) throw new \Exception(trim(implode(" ", $errors)));
    }
}

The problem I have here is that in the PHPUnit test method I check for different combinations. This causes tests to pass that I intend to fail.

/**
 * @expectedException \Exception
 * @expectedExceptionMessage a < b.
 */
public function testValues_ALessBOnly()
{
    $myClass = new MyClass()
    $myClass->validate(1, 2, 4, 3);
}

The string of the Exception message is actually "a < b. b < c." but this test still passes. I intend for this test to fail because the message is not exactly what I expect.

Is there a way with PHPUnit to expect an exact string, rather than a substring? I hope to avoid the following:

public function testValues_ALessBOnly()
{
    $myClass = new MyClass()
    $fail = FALSE;

    try
    {
        $myClass->validate(1, 2, 4, 3);
    }
    catch(\Exception $e)
    {
        $fail = TRUE;
        $this->assertEquals($e->getMessage(), "a < b.";
    }

    if(!$fail) $this->fail("No Exceptions were thrown.");
}

Answer 1

You can use $this->expectExceptionMessage() to handle this.

Example:

$this->expectException(InvalidArgumentException::class);
$this->expectExceptionMessage('Some error message');

Answer 2

When this question was posted, PHPUnit v3.7 didn't have a solution to this problem. Newer versions have a new @expectedExceptionMessageRegExp option that you can use to add a regular expression to match the exception message against.

Your case, using ^ and $ to force the string to be exactly what is expected, could look like this:

/**
 * @expectedException \Exception
 * @expectedExceptionMessageRegExp /^a < b\.$/
 */
public function testValues_ALessBOnly()
{
    $myClass = new MyClass()
    $myClass->validate(1, 2, 4, 3);
}