Fail on error by default during test AOT processing

Prior to this commit, if an error was encountered during build-time AOT
processing, the error was logged at WARN/DEBUG level, and processing
continued.

With this commit, test AOT processing now fails on error by default. In
addition, the `failOnError` mode can be disabled by setting the
`spring.test.aot.processing.failOnError` Spring/System property to
`false`.

Closes gh-30977

spring-test/src/test/java/org/springframework/test/context/aot/AotIntegrationTests.java

@@ -87,7 +87,7 @@ class AotIntegrationTests extends AbstractAotTests {
 
 		// AOT BUILD-TIME: PROCESSING
 		InMemoryGeneratedFiles generatedFiles = new InMemoryGeneratedFiles();
-		TestContextAotGenerator generator = new TestContextAotGenerator(generatedFiles, new RuntimeHints(), true);
+		TestContextAotGenerator generator = new TestContextAotGenerator(generatedFiles, new RuntimeHints());
 		generator.processAheadOfTime(testClasses);
 
 		List<String> sourceFiles = generatedFiles.getGeneratedFiles(Kind.SOURCE).keySet().stream().toList();

spring-test/src/test/java/org/springframework/test/context/aot/TestContextAotGeneratorUnitTests.java

@@ -0,0 +1,68 @@
+/*
+ * 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.aot;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import org.springframework.core.SpringProperties;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.context.aot.TestContextAotGenerator.FAIL_ON_ERROR_PROPERTY_NAME;
+
+/**
+ * Unit tests for {@link TestContextAotGenerator}.
+ *
+ * @author Sam Brannen
+ * @since 6.1
+ */
+class TestContextAotGeneratorUnitTests {
+
+	@BeforeEach
+	@AfterEach
+	void resetFlag() {
+		SpringProperties.setProperty(FAIL_ON_ERROR_PROPERTY_NAME, null);
+	}
+
+	@Test
+	void failOnErrorEnabledByDefault() {
+		assertThat(createGenerator().failOnError).isTrue();
+	}
+
+	@ParameterizedTest
+	@ValueSource(strings = {"true", "  True\t"})
+	void failOnErrorEnabledViaSpringProperty(String value) {
+		SpringProperties.setProperty(FAIL_ON_ERROR_PROPERTY_NAME, value);
+		assertThat(createGenerator().failOnError).isTrue();
+	}
+
+	@ParameterizedTest
+	@ValueSource(strings = {"false", "  False\t", "x"})
+	void failOnErrorDisabledViaSpringProperty(String value) {
+		SpringProperties.setProperty(FAIL_ON_ERROR_PROPERTY_NAME, value);
+		assertThat(createGenerator().failOnError).isFalse();
+	}
+
+
+	private static TestContextAotGenerator createGenerator() {
+		return new TestContextAotGenerator(null);
+	}
+
+}