Add MockSpringFactoriesLoader

Add a `MockSpringFactoriesLoader` class which allows for easier
testing of code that works with a `SpringFactoriesLoader`.

Closes gh-28416

spring-core-test/src/test/java/org/springframework/core/mock/MockSpringFactoriesLoaderTests.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2002-2022 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.core.mock;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.annotation.Order;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link MockSpringFactoriesLoader}.
+ *
+ * @author Phillip Webb
+ */
+class MockSpringFactoriesLoaderTests {
+
+	@Test
+	void addWithClassesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.add(TestFactoryType.class, TestFactoryOne.class, TestFactoryTwo.class);
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	@Test
+	void addWithClassNamesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.add(TestFactoryType.class.getName(), TestFactoryOne.class.getName(), TestFactoryTwo.class.getName());
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	@Test
+	void addWithClassAndInstancesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.addInstance(TestFactoryType.class, new TestFactoryOne(), new TestFactoryTwo());
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	@Test
+	void addWithClassNameAndInstancesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.addInstance(TestFactoryType.class.getName(), new TestFactoryOne(), new TestFactoryTwo());
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	private void assertThatLoaderHasTestFactories(MockSpringFactoriesLoader loader) {
+		List<TestFactoryType> factories = loader.load(TestFactoryType.class);
+		assertThat(factories).hasSize(2);
+		assertThat(factories.get(0)).isInstanceOf(TestFactoryOne.class);
+		assertThat(factories.get(1)).isInstanceOf(TestFactoryTwo.class);
+	}
+
+	static interface TestFactoryType {
+
+	}
+
+	@Order(1)
+	static class TestFactoryOne implements TestFactoryType {
+
+	}
+
+	@Order(2)
+	static class TestFactoryTwo implements TestFactoryType {
+
+	}
+
+}