checkNotNull(runnable, "Runnable was null.");
    checkNotNull(executor, "Executor was null.");

    // Lock while we check state. We must maintain the lock while adding the new pair so that
    // another thread can't run the list out from under us. We only add to the list if we have not
    // yet started execution.
    synchronized (this) {
      if (!executed) {

 *
 * <p>When iterating through the collections supplied by this class, the ordering of values for a
 * given key agrees with the order in which the values were added.
 *
 * <p>This multimap allows duplicate key-value pairs. After adding a new key-value pair equal to an
 * existing key-value pair, the {@code ArrayListMultimap} will contain entries for both the new
 * value and the old value.
 *

 * keys according to the above key ordering, and for each key they iterate across the values
 * according to the value ordering.
 *
 * <p>The multimap does not store duplicate key-value pairs. Adding a new key-value pair equal to an
 * existing key-value pair has no effect.
 *
 * <p>Null keys and values are permitted (provided, of course, that the respective comparators

    [the Android flavor](https://github.com/google/guava/wiki/Android). You can
    find the Android Guava source in the [`android` directory].

[`android` directory]: https://github.com/google/guava/tree/master/android

## Adding Guava to your build

Guava's Maven group ID is `com.google.guava`, and its artifact ID is `guava`.
Guava provides two different "flavors": one for use on a (Java 8+) JRE and one

# Guava Testlib: Google Testing Libraries for Java

Guava testlib is a set of Java classes for more convenient
unit testing.

## Adding Guava Testlib to your build

Guava testlib's Maven group ID is `com.google.guava` and its artifact ID is `guava-testlib`.

To add a dependency on Guava testlib using Maven, use the following:

```xml
<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava-testlib</artifactId>

 *
 * <p>When iterating through the collections supplied by this class, the ordering of values for a
 * given key agrees with the order in which the values were added.
 *
 * <p>This multimap allows duplicate key-value pairs. After adding a new key-value pair equal to an
 * existing key-value pair, the {@code ArrayListMultimap} will contain entries for both the new
 * value and the old value.
 *