Add support for property file encoding in @TestPropertySource

Prior to this commit, property files configured (or inferred) via
@TestPropertySource were read using the default encoding of the JVM.

This commit introduces an `encoding` attribute in @TestPropertySource
which allows developers to specify an explicit encoding for test
property files.

Closes gh-30982

spring-test/src/main/java/org/springframework/test/context/MergedContextConfiguration.java

@@ -395,6 +395,7 @@ public class MergedContextConfiguration implements Serializable {
 	 * {@code PropertySources}.
 	 * @since 6.1
 	 * @see TestPropertySource#locations
+	 * @see TestPropertySource#encoding
 	 * @see TestPropertySource#factory
 	 */
 	public List<PropertySourceDescriptor> getPropertySourceDescriptors() {

spring-test/src/main/java/org/springframework/test/context/TestPropertySource.java

@@ -145,6 +145,7 @@ public @interface TestPropertySource {
 	 * @see #inheritLocations
 	 * @see #value
 	 * @see #properties
+	 * @see #encoding
 	 * @see #factory
 	 * @see org.springframework.core.env.PropertySource
 	 */
@@ -280,6 +281,14 @@ public @interface TestPropertySource {
 	 */
 	boolean inheritProperties() default true;
 
+	/**
+	 * Specify the character encoding for the given {@linkplain #locations resources}
+	 * — for example, "UTF-8".
+	 * <p>If not specified, the default character encoding of the JVM will be used.
+	 * @since 6.1
+	 */
+	String encoding() default "";
+
 	/**
 	 * Specify a custom {@link PropertySourceFactory}, if any.
 	 * <p>By default, a factory for standard resource files will be used which

spring-test/src/main/java/org/springframework/test/context/support/MergedTestPropertySources.java

@@ -70,7 +70,9 @@ class MergedTestPropertySources {
 
 	/**
 	 * Get the descriptors for resource locations of properties files.
-	 * @see TestPropertySource#locations()
+	 * @see TestPropertySource#locations
+	 * @see TestPropertySource#encoding
+	 * @see TestPropertySource#factory
 	 */
 	List<PropertySourceDescriptor> getPropertySourceDescriptors() {
 		return this.descriptors;

spring-test/src/main/java/org/springframework/test/context/support/TestPropertySourceAttributes.java

@@ -126,22 +126,28 @@ class TestPropertySourceAttributes {
 				TestContextResourceUtils.convertToClasspathResourcePaths(declaringClass, true, locations);
 		Class<? extends PropertySourceFactory> factoryClass =
 				(Class<? extends PropertySourceFactory>) mergedAnnotation.getClass("factory");
+		String encoding = mergedAnnotation.getString("encoding");
+		if (encoding.isBlank()) {
+			encoding = null; // default encoding will be inferred
+		}
 		PropertySourceDescriptor descriptor = new PropertySourceDescriptor(
-				Arrays.asList(convertedLocations), false, null, factoryClass, null);
+				List.of(convertedLocations), false, null, factoryClass, encoding);
-		addPropertiesAndLocations(List.of(descriptor), properties, declaringClass, false);
+		addPropertiesAndLocations(List.of(descriptor), properties, declaringClass, encoding, false);
 	}
 
 	private void mergePropertiesAndLocationsFrom(TestPropertySourceAttributes attributes) {
 		addPropertiesAndLocations(attributes.getPropertySourceDescriptors(), attributes.getProperties(),
-				attributes.getDeclaringClass(), true);
+				attributes.getDeclaringClass(), null, true);
 	}
 
 	private void addPropertiesAndLocations(List<PropertySourceDescriptor> descriptors, String[] properties,
-			Class<?> declaringClass, boolean prepend) {
+			Class<?> declaringClass, String encoding, boolean prepend) {
 
 		if (hasNoLocations(descriptors) && ObjectUtils.isEmpty(properties)) {
 			String defaultPropertiesFile = detectDefaultPropertiesFile(declaringClass);
-			addAll(prepend, this.descriptors, List.of(new PropertySourceDescriptor(defaultPropertiesFile)));
+			PropertySourceDescriptor descriptor = new PropertySourceDescriptor(
+					List.of(defaultPropertiesFile), false, null, null, encoding);
+			addAll(prepend, this.descriptors, List.of(descriptor));
 		}
 		else {
 			addAll(prepend, this.descriptors, descriptors);

spring-test/src/test/java/org/springframework/test/context/env/CustomEncodingTestPropertySourceTests.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2002-2023 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.test.context.env;
+
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.env.Environment;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for {@link TestPropertySource @TestPropertySource} support
+ * with custom resource encoding.
+ *
+ * @author Sam Brannen
+ * @since 6.1
+ */
+@SpringJUnitConfig
+class CustomEncodingTestPropertySourceTests {
+
+	@Nested
+	@TestPropertySource(locations = "test-ISO-8859-1.properties", encoding = "UTF-8" )
+	@DirtiesContext
+	class IncorrectEncodingTests {
+
+		@Test
+		void propertyIsAvailableInEnvironment(@Autowired Environment env) {
+			// The "é" characters in "Générales" get converted to U+FFFD : REPLACEMENT CHARACTER.
+			assertThat(env.getProperty("text")).isEqualTo("G\uFFFDn\uFFFDrales");
+		}
+	}
+
+	@Nested
+	@TestPropertySource(locations = "test-ISO-8859-1.properties", encoding = "ISO-8859-1" )
+	@DirtiesContext
+	class ExplicitEncodingTests {
+
+		@Test
+		void propertyIsAvailableInEnvironment(@Autowired Environment env) {
+			assertThat(env.getProperty("text")).isEqualTo("Générales");
+		}
+	}
+
+
+	@Configuration
+	static class Config {
+		/* no user beans required for these tests */
+	}
+
+}

spring-test/src/test/resources/org/springframework/test/context/env/test-ISO-8859-1.properties

@@ -0,0 +1,2 @@
+# This file is saved using ISO-8859-1 encoding
+text=Générales