Feature/template unit test (#958)

* add HeaderTemplate create tests for fail

* - added expand test

* - remove redundant public static identifier from Retryer inner class

* - remove redundant public static identifier from Default inner class

* add license to test

* mvn clean install to format test file

core/src/main/java/feign/Client.java

@@ -48,7 +48,7 @@ public interface Client {
    */
   Response execute(Request request, Options options) throws IOException;
 
-  public static class Default implements Client {
+  class Default implements Client {
 
     private final SSLSocketFactory sslContextFactory;
     private final HostnameVerifier hostnameVerifier;

core/src/main/java/feign/Retryer.java

@@ -26,7 +26,7 @@ public interface Retryer extends Cloneable {
 
   Retryer clone();
 
-  public static class Default implements Retryer {
+  class Default implements Retryer {
 
     private final int maxAttempts;
     private final long period;

core/src/test/java/feign/template/HeaderTemplateTest.java

@@ -0,0 +1,60 @@
+/**
+ * Copyright 2012-2019 The Feign Authors
+ *
+ * <p>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
+ *
+ * <p>http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * <p>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 feign.template;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Arrays;
+import java.util.Collections;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+public class HeaderTemplateTest {
+
+  @Rule public ExpectedException exception = ExpectedException.none();
+
+  @Test(expected = IllegalArgumentException.class)
+  public void it_should_throw_exception_when_name_is_null() {
+    HeaderTemplate.create(null, Arrays.asList("test"));
+    exception.expectMessage("name is required.");
+  }
+
+  @Test(expected = IllegalArgumentException.class)
+  public void it_should_throw_exception_when_name_is_empty() {
+    HeaderTemplate.create("", Arrays.asList("test"));
+    exception.expectMessage("name is required.");
+  }
+
+  @Test(expected = IllegalArgumentException.class)
+  public void it_should_throw_exception_when_value_is_null() {
+    HeaderTemplate.create("test", null);
+    exception.expectMessage("values are required");
+  }
+
+  @Test
+  public void it_should_return_name() {
+    HeaderTemplate headerTemplate =
+        HeaderTemplate.create("test", Arrays.asList("test 1", "test 2"));
+    assertEquals("test", headerTemplate.getName());
+  }
+
+  @Test
+  public void it_should_return_expanded() {
+    HeaderTemplate headerTemplate = HeaderTemplate.create("hello", Arrays.asList("emre", "savci"));
+    assertEquals("hello emre, savci", headerTemplate.expand(Collections.emptyMap()));
+    assertEquals(
+        "hello emre, savci", headerTemplate.expand(Collections.singletonMap("name", "firsts")));
+  }
+}