Add dedicated ApiVersionResolver implementations

Closes gh-35747

spring-web/src/test/java/org/springframework/web/accept/HeaderApiVersionResolverTests.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2002-present 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.web.accept;
+
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for {@link HeaderApiVersionResolver}.
+ * @author Rossen Stoyanchev
+ */
+public class HeaderApiVersionResolverTests {
+
+	private final String headerName = "Api-Version";
+
+	private final HeaderApiVersionResolver resolver = new HeaderApiVersionResolver(headerName);
+
+
+	@Test
+	void resolve() {
+		String version = "1.2";
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/path");
+		request.addHeader(headerName, version);
+		String actual = resolver.resolveVersion(request);
+		assertThat(actual).isEqualTo(version);
+	}
+
+	@Test
+	void noHeader() {
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/path");
+		String version = resolver.resolveVersion(request);
+		assertThat(version).isNull();
+	}
+
+}