Resolve ContextLoader only once in AbstractTestContextBootstrapper

Closes gh-35994

Author: sbrannen

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

@@ -231,7 +231,7 @@ public final MergedContextConfiguration buildMergedContextConfiguration() {
 Class<?> declaringClass = reversedList.get(0).getDeclaringClass();
 
 mergedConfig = buildMergedContextConfiguration(
-declaringClass, reversedList, parentConfig, cacheAwareContextLoaderDelegate, true);
+declaringClass, reversedList, null, parentConfig, cacheAwareContextLoaderDelegate, true);
 parentConfig = mergedConfig;
 }
 
@@ -242,7 +242,7 @@ public final MergedContextConfiguration buildMergedContextConfiguration() {
 else {
 return buildMergedContextConfiguration(testClass,
 ContextLoaderUtils.resolveContextConfigurationAttributes(testClass),
-null, cacheAwareContextLoaderDelegate, true);
+null, null, cacheAwareContextLoaderDelegate, true);
 }
 }
 
@@ -263,7 +263,7 @@ else if (logger.isDebugEnabled()) {
 "Neither @ContextConfiguration nor @ContextHierarchy found for test class [%s]: using %s",
 testClass.getSimpleName(), contextLoader.getClass().getSimpleName()));
 }
-return buildMergedContextConfiguration(testClass, defaultConfigAttributesList, null,
+return buildMergedContextConfiguration(testClass, defaultConfigAttributesList, contextLoader, null,
 cacheAwareContextLoaderDelegate, false);
 }
 
@@ -277,6 +277,7 @@ else if (logger.isDebugEnabled()) {
  * specified test class, ordered <em>bottom-up</em> (i.e., as if we were
  * traversing up the class hierarchy and enclosing class hierarchy); never
  * {@code null} or empty
+ * @param contextLoader a pre-resolved {@link ContextLoader} to use; may be {@code null}
  * @param parentConfig the merged context configuration for the parent application
  * context in a context hierarchy, or {@code null} if there is no parent
  * @param cacheAwareContextLoaderDelegate the cache-aware context loader delegate to
@@ -294,13 +295,16 @@ else if (logger.isDebugEnabled()) {
  * @see MergedContextConfiguration
  */
 private MergedContextConfiguration buildMergedContextConfiguration(Class<?> testClass,
-List<ContextConfigurationAttributes> configAttributesList, @Nullable MergedContextConfiguration parentConfig,
+List<ContextConfigurationAttributes> configAttributesList, @Nullable ContextLoader contextLoader,
+@Nullable MergedContextConfiguration parentConfig,
 CacheAwareContextLoaderDelegate cacheAwareContextLoaderDelegate,
 boolean requireLocationsClassesOrInitializers) {
 
 Assert.notEmpty(configAttributesList, "ContextConfigurationAttributes list must not be null or empty");
 
-ContextLoader contextLoader = resolveContextLoader(testClass, configAttributesList);
+if (contextLoader == null) {
+contextLoader = resolveContextLoader(testClass, configAttributesList);
+}
 List<String> locations = new ArrayList<>();
 List<Class<?>> classes = new ArrayList<>();
 List<Class<?>> initializers = new ArrayList<>();
@@ -331,11 +335,12 @@ private MergedContextConfiguration buildMergedContextConfiguration(Class<?> test
 Set<ContextCustomizer> contextCustomizers = getContextCustomizers(testClass,
 Collections.unmodifiableList(configAttributesList));
 
+ContextLoader effectivelyFinalContextLoader = contextLoader;
 Assert.state(!(requireLocationsClassesOrInitializers &&
-areAllEmpty(locations, classes, initializers, contextCustomizers)), () -> String.format(
-"%s was unable to detect defaults, and no ApplicationContextInitializers " +
-"or ContextCustomizers were declared for context configuration attributes %s",
-contextLoader.getClass().getSimpleName(), configAttributesList));
+areAllEmpty(locations, classes, initializers, contextCustomizers)), () -> """
+%s was unable to detect defaults, and no ApplicationContextInitializers \
+or ContextCustomizers were declared for context configuration attributes %s\
+""".formatted(effectivelyFinalContextLoader.getClass().getSimpleName(), configAttributesList));
 
 MergedTestPropertySources mergedTestPropertySources =
 TestPropertySourceUtils.buildMergedTestPropertySources(testClass);