Add test for potion durations

projects/core/src/testFixtures/java/dan200/computercraft/test/core/CustomMatchers.java

@@ -5,11 +5,14 @@
 package dan200.computercraft.test.core;
 
 import org.hamcrest.Matcher;
+import org.hamcrest.StringDescription;
 
 import java.util.List;
+import java.util.Map;
 import java.util.function.Function;
 
 import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.is;
 
 public class CustomMatchers {
     /**
@@ -25,4 +28,32 @@ public class CustomMatchers {
     public static <T> Matcher<Iterable<? extends T>> containsWith(List<T> items, Function<T, Matcher<? super T>> matcher) {
         return contains(items.stream().map(matcher).toList());
     }
+
+    /**
+     * An alternative to {@link org.hamcrest.Matchers#hasEntry(Object, Object)}, that acts as a projection, rather than
+     * searching the map.
+     *
+     * @param key   The key to extract.
+     * @param value The expected value.
+     * @param <K>   The type of keys in the map.
+     * @param <V>   The type of values in the map.
+     * @return A matcher that projects out of a map.
+     */
+    public static <K, V> Matcher<Map<? extends K, ? extends V>> containsEntry(K key, V value) {
+        return containsEntryWith(key, is(value));
+    }
+
+    /**
+     * An alternative to {@link org.hamcrest.Matchers#hasEntry(Matcher, Matcher)}, that acts as a projection, rather
+     * than searching the map.
+     *
+     * @param key   The key to extract.
+     * @param value The expected value.
+     * @param <K>   The type of keys in the map.
+     * @param <V>   The type of values in the map.
+     * @return A matcher that projects out of a map.
+     */
+    public static <K, V> Matcher<Map<? extends K, ? extends V>> containsEntryWith(K key, Matcher<? super V> value) {
+        return ContramapMatcher.contramap(value, new StringDescription().appendValue(key).toString(), x -> x.get(key));
+    }
 }