Move WindowMatchers to main component of runners-core

Author: kennknowles

runners/core-java/build.gradle

@@ -48,6 +48,7 @@ dependencies {
   implementation library.java.slf4j_api
   implementation library.java.jackson_core
   implementation library.java.jackson_databind
+  implementation library.java.hamcrest
   testImplementation project(path: ":sdks:java:core", configuration: "shadowTest")
   testImplementation library.java.junit
   testImplementation library.java.mockito_core

runners/core-java/src/test/java/org/apache/beam/runners/core/WindowMatchers.java renamed to runners/core-java/src/main/java/org/apache/beam/runners/core/WindowMatchers.java

@@ -20,6 +20,7 @@
 import java.util.Collection;
 import java.util.Objects;
 import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
+import org.apache.beam.sdk.transforms.windowing.GlobalWindow;
 import org.apache.beam.sdk.transforms.windowing.IntervalWindow;
 import org.apache.beam.sdk.transforms.windowing.PaneInfo;
 import org.apache.beam.sdk.values.WindowedValue;
@@ -31,6 +32,9 @@
 import org.joda.time.Instant;
 
 /** Matchers that are useful for working with Windowing, Timestamps, etc. */
+@SuppressWarnings({
+  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
+})
 public class WindowMatchers {
 
   public static <T> Matcher<WindowedValue<? extends T>> isWindowedValue(
@@ -166,6 +170,11 @@ protected void describeMismatchSafely(
     };
   }
 
+  public static <T> Matcher<WindowedValue<? extends T>> isValueInGlobalWindow(
+      T value, Instant timestamp) {
+    return isSingleWindowedValue(value, timestamp, GlobalWindow.INSTANCE);
+  }
+
   @SuppressWarnings({"unchecked", "rawtypes"})
   @SafeVarargs
   public static final <W extends BoundedWindow> Matcher<Iterable<W>> ofWindows(