Add the org.springframework.geode.util.GeodeAssertions abstract class containing assertions for different Apache Geode objects, such as a cache or Region.

GeodeAssertions will help in the effort to remove all uses of internal Apache Geode APIs and restrict all internal Apache Geode API usage to the apache-geode-extensions module.

Resolves gh-70.

apache-geode-extensions/src/main/java/org/springframework/geode/util/GeodeAssertions.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+package org.springframework.geode.util;
+
+import org.apache.geode.cache.GemFireCache;
+import org.apache.geode.cache.Region;
+import org.apache.geode.internal.cache.AbstractRegion;
+import org.apache.geode.internal.cache.GemFireCacheImpl;
+
+/**
+ * Abstract utility class containing different assertions for Apache Geode objects, such as a {@link GemFireCache}
+ * or {@link Region}, and so on.
+ *
+ * @author John Blum
+ * @see org.apache.geode.cache.GemFireCache
+ * @see org.apache.geode.cache.Region
+ * @since 1.3.0
+ */
+@SuppressWarnings("unused")
+public abstract class GeodeAssertions {
+
+	public static <T> AssertThat<T> assertThat(T obj) {
+		return () -> obj;
+	}
+
+	private static Class<?> nullSafeType(Object obj) {
+		return obj != null ? obj.getClass() : null;
+	}
+
+	private static String nullSafeTypeName(Class<?> type) {
+		return type != null ? type.getName() : null;
+	}
+
+	public static String nullSafeTypeName(Object obj) {
+		return nullSafeTypeName(nullSafeType(obj));
+	}
+
+	@FunctionalInterface
+	public interface AssertThat<T> {
+
+		T getSubject();
+
+		default void isNotInstanceOfAbstractRegion() {
+
+			Object subject = getSubject();
+
+			if (subject instanceof AbstractRegion) {
+				throw new AssertionError(String.format("[%1$s] is an instance of [%2$s]",
+					nullSafeTypeName(subject), AbstractRegion.class.getName()));
+			}
+		}
+
+		default void isNotInstanceOfGemFireCacheImpl() {
+
+			Object subject = getSubject();
+
+			if (subject instanceof GemFireCacheImpl) {
+				throw new AssertionError(String.format("[%1$s] is an instance of [%2$s]",
+					nullSafeTypeName(subject), GemFireCacheImpl.class.getName()));
+			}
+		}
+	}
+}