/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.apache.commons.configuration2.interpol;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertFalse;
  import static org.junit.jupiter.api.Assertions.assertNotNull;
  import static org.junit.jupiter.api.Assertions.assertNotSame;
  import static org.junit.jupiter.api.Assertions.assertNull;
  import static org.junit.jupiter.api.Assertions.assertSame;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  import static org.junit.jupiter.api.Assertions.assertTrue;
  import static org.mockito.ArgumentMatchers.any;
  import static org.mockito.Mockito.mock;
  import static org.mockito.Mockito.verify;
  import static org.mockito.Mockito.verifyNoInteractions;
  import static org.mockito.Mockito.verifyNoMoreInteractions;
  import static org.mockito.Mockito.when;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.EnumSet;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Properties;
  import java.util.Set;
  import java.util.function.Function;
  
  import org.apache.commons.text.lookup.StringLookupFactory;
  import org.junit.jupiter.api.BeforeEach;
  import org.junit.jupiter.api.Test;
  
  /**
   * Test class for ConfigurationInterpolator.
   */
  public class TestConfigurationInterpolator {
  
      /** Constant for a test variable name. */
      private static final String TEST_NAME = "varname";
  
      /** Constant for a test variable prefix. */
      private static final String TEST_PREFIX = "prefix";
  
      /** Constant for the value of the test variable. */
      private static final String TEST_VALUE = "TestVariableValue";
  
      private static void assertMappedLookups(final Map<String, Lookup> lookupMap, final String... keys) {
          final Set<String> remainingKeys = new HashSet<>(lookupMap.keySet());
  
          for (final String key : keys) {
              assertNotNull(key, "Expected map to contain string lookup for key " + key);
  
              remainingKeys.remove(key);
          }
  
          assertEquals(Collections.emptySet(), remainingKeys);
      }
  
      private static void checkDefaultPrefixLookupsHolder(final Properties props, final String... keys) {
          final ConfigurationInterpolator.DefaultPrefixLookupsHolder holder =
                  new ConfigurationInterpolator.DefaultPrefixLookupsHolder(props);
  
          final Map<String, Lookup> lookupMap = holder.getDefaultPrefixLookups();
  
          assertMappedLookups(lookupMap, keys);
      }
  
      /**
       * Main method used to verify the default lookups resolved during JVM execution.
       * @param args
       */
      public static void main(final String[] args) {
          System.out.println("Default lookups");
          for (final String key : ConfigurationInterpolator.getDefaultPrefixLookups().keySet()) {
              System.out.println("- " + key);
          }
      }
  
      /**
       * Creates a lookup object that can resolve the test variable (and nothing else).
      *
      * @return the test lookup object
      */
     private static Lookup setUpTestLookup() {
         return setUpTestLookup(TEST_NAME, TEST_VALUE);
     }
 
     /**
      * Creates a lookup object that can resolve the specified variable (and nothing else).
      *
      * @param var the variable name
      * @param value the value of this variable
      * @return the test lookup object
      */
     private static Lookup setUpTestLookup(final String var, final Object value) {
         final Lookup lookup = mock(Lookup.class);
         when(lookup.lookup(any())).thenAnswer(invocation -> {
             if (var.equals(invocation.getArgument(0))) {
                 return value;
             }
             return null;
         });
         return lookup;
     }
 
     /** Stores the object to be tested. */
     private ConfigurationInterpolator interpolator;
 
     @BeforeEach
     public void setUp() throws Exception {
         interpolator = new ConfigurationInterpolator();
     }
 
     /**
      * Tests whether multiple default lookups can be added.
      */
     @Test
     void testAddDefaultLookups() {
         final List<Lookup> lookups = new ArrayList<>();
         lookups.add(setUpTestLookup());
         lookups.add(setUpTestLookup("test", "value"));
         interpolator.addDefaultLookups(lookups);
         final List<Lookup> lookups2 = interpolator.getDefaultLookups();
         assertEquals(lookups, lookups2);
     }
 
     /**
      * Tests whether a null collection of default lookups is handled correctly.
      */
     @Test
     void testAddDefaultLookupsNull() {
         interpolator.addDefaultLookups(null);
         assertTrue(interpolator.getDefaultLookups().isEmpty());
     }
 
     @Test
     void testDefaultStringLookupsHolderAllLookups() {
         final Properties props = new Properties();
         props.setProperty(ConfigurationInterpolator.DEFAULT_PREFIX_LOOKUPS_PROPERTY,
                 "BASE64_DECODER BASE64_ENCODER const, date, dns, environment "
                 + "file ,java, local_host properties, resource_bundle,script,system_properties "
                 + "url url_decoder  , url_encoder, xml");
 
         checkDefaultPrefixLookupsHolder(props,
                 "base64",
                 StringLookupFactory.KEY_BASE64_DECODER,
                 StringLookupFactory.KEY_BASE64_ENCODER,
                 StringLookupFactory.KEY_CONST,
                 StringLookupFactory.KEY_DATE,
                 StringLookupFactory.KEY_ENV,
                 StringLookupFactory.KEY_FILE,
                 StringLookupFactory.KEY_JAVA,
                 StringLookupFactory.KEY_LOCALHOST,
                 StringLookupFactory.KEY_PROPERTIES,
                 StringLookupFactory.KEY_RESOURCE_BUNDLE,
                 StringLookupFactory.KEY_SYS,
                 StringLookupFactory.KEY_URL_DECODER,
                 StringLookupFactory.KEY_URL_ENCODER,
                 StringLookupFactory.KEY_XML,
 
                 StringLookupFactory.KEY_DNS,
                 StringLookupFactory.KEY_URL,
                 StringLookupFactory.KEY_SCRIPT);
     }
 
     @Test
     void testDefaultStringLookupsHolderGivenSingleLookup() {
         final Properties props = new Properties();
         props.setProperty(ConfigurationInterpolator.DEFAULT_PREFIX_LOOKUPS_PROPERTY, "base64_encoder");
         checkDefaultPrefixLookupsHolder(props, "base64", StringLookupFactory.KEY_BASE64_ENCODER);
     }
 
     @Test
     void testDefaultStringLookupsHolderGivenSingleLookupWeirdString() {
         final Properties props = new Properties();
         props.setProperty(ConfigurationInterpolator.DEFAULT_PREFIX_LOOKUPS_PROPERTY, " \n \t  ,, DnS , , ");
         checkDefaultPrefixLookupsHolder(props, StringLookupFactory.KEY_DNS);
     }
 
     @Test
     void testDefaultStringLookupsHolderInvalidLookupsDefinition() {
         final Properties props = new Properties();
         props.setProperty(ConfigurationInterpolator.DEFAULT_PREFIX_LOOKUPS_PROPERTY, "base64_encoder nope");
         final Exception exc = assertThrows(Exception.class, () -> new ConfigurationInterpolator.DefaultPrefixLookupsHolder(props));
         assertEquals("Invalid default lookups definition: base64_encoder nope", exc.getMessage());
     }
 
     @Test
     void testDefaultStringLookupsHolderLookupsPropertyEmptyAndBlank() {
         final Properties propsWithNull = new Properties();
         propsWithNull.setProperty(ConfigurationInterpolator.DEFAULT_PREFIX_LOOKUPS_PROPERTY, "");
 
         checkDefaultPrefixLookupsHolder(propsWithNull);
 
         final Properties propsWithBlank = new Properties();
         propsWithBlank.setProperty(ConfigurationInterpolator.DEFAULT_PREFIX_LOOKUPS_PROPERTY, " ");
 
         checkDefaultPrefixLookupsHolder(propsWithBlank);
     }
 
     @Test
     void testDefaultStringLookupsHolderLookupsPropertyNotPresent() {
         checkDefaultPrefixLookupsHolder(new Properties(),
                 "base64",
                 StringLookupFactory.KEY_BASE64_DECODER,
                 StringLookupFactory.KEY_BASE64_ENCODER,
                 StringLookupFactory.KEY_CONST,
                 StringLookupFactory.KEY_DATE,
                 StringLookupFactory.KEY_ENV,
                 StringLookupFactory.KEY_FILE,
                 StringLookupFactory.KEY_JAVA,
                 StringLookupFactory.KEY_LOCALHOST,
                 StringLookupFactory.KEY_PROPERTIES,
                 StringLookupFactory.KEY_RESOURCE_BUNDLE,
                 StringLookupFactory.KEY_SYS,
                 StringLookupFactory.KEY_URL_DECODER,
                 StringLookupFactory.KEY_URL_ENCODER,
                 StringLookupFactory.KEY_XML);
     }
 
     @Test
     void testDefaultStringLookupsHolderMultipleLookups() {
         final Properties props = new Properties();
         props.setProperty(ConfigurationInterpolator.DEFAULT_PREFIX_LOOKUPS_PROPERTY, "dns, url script ");
 
         checkDefaultPrefixLookupsHolder(props,
                 StringLookupFactory.KEY_DNS,
                 StringLookupFactory.KEY_URL,
                 StringLookupFactory.KEY_SCRIPT);
     }
 
     /**
      * Tests deregistering a lookup object.
      */
     @Test
     void testDeregisterLookup() {
         final Lookup lookup = mock(Lookup.class);
         interpolator.registerLookup(TEST_PREFIX, lookup);
         assertTrue(interpolator.deregisterLookup(TEST_PREFIX));
         assertFalse(interpolator.prefixSet().contains(TEST_PREFIX));
         assertTrue(interpolator.getLookups().isEmpty());
     }
 
     /**
      * Tests deregistering an unknown lookup object.
      */
     @Test
     void testDeregisterLookupNonExisting() {
         assertFalse(interpolator.deregisterLookup(TEST_PREFIX));
     }
 
     /**
      * Tests whether the flag for substitution in variable names can be modified.
      */
     @Test
     void testEnableSubstitutionInVariables() {
         assertFalse(interpolator.isEnableSubstitutionInVariables());
         interpolator.addDefaultLookup(setUpTestLookup("java.version", "1.4"));
         interpolator.addDefaultLookup(setUpTestLookup("jre-1.4", "C:\\java\\1.4"));
         final String var = "${jre-${java.version}}";
         assertEquals(var, interpolator.interpolate(var));
         interpolator.setEnableSubstitutionInVariables(true);
         assertTrue(interpolator.isEnableSubstitutionInVariables());
         assertEquals("C:\\java\\1.4", interpolator.interpolate(var));
     }
 
     /**
      * Tests fromSpecification() if the specification contains an instance.
      */
     @Test
     void testFromSpecificationInterpolator() {
         final ConfigurationInterpolator ci = mock(ConfigurationInterpolator.class);
         final InterpolatorSpecification spec = new InterpolatorSpecification.Builder().withDefaultLookup(mock(Lookup.class))
             .withParentInterpolator(interpolator).withInterpolator(ci).create();
         assertSame(ci, ConfigurationInterpolator.fromSpecification(spec));
     }
 
     /**
      * Tests fromSpecification() if a new instance has to be created.
      */
     @Test
     void testFromSpecificationNewInstance() {
         final Lookup defLookup = mock(Lookup.class);
         final Lookup preLookup = mock(Lookup.class);
         final Function<Object, String> stringConverter = obj -> Objects.toString(obj, null);
         final InterpolatorSpecification spec = new InterpolatorSpecification.Builder()
             .withDefaultLookup(defLookup)
             .withPrefixLookup("p", preLookup)
             .withParentInterpolator(interpolator)
             .withStringConverter(stringConverter)
             .create();
         final ConfigurationInterpolator ci = ConfigurationInterpolator.fromSpecification(spec);
         assertEquals(Arrays.asList(defLookup), ci.getDefaultLookups());
         assertEquals(1, ci.getLookups().size());
         assertSame(preLookup, ci.getLookups().get("p"));
         assertSame(interpolator, ci.getParentInterpolator());
         assertSame(stringConverter, ci.getStringConverter());
     }
 
     /**
      * Tries to obtain an instance from a null specification.
      */
     @Test
     void testFromSpecificationNull() {
         assertThrows(IllegalArgumentException.class, () -> ConfigurationInterpolator.fromSpecification(null));
     }
 
     /**
      * Tests whether modification of the list of default lookups does not affect the object.
      */
     @Test
     void testGetDefaultLookupsModify() {
         final List<Lookup> lookups = interpolator.getDefaultLookups();
         lookups.add(setUpTestLookup());
         assertTrue(interpolator.getDefaultLookups().isEmpty());
     }
 
     /**
      * Tests whether default prefix lookups can be queried as a map.
      */
     @Test
     void testGetDefaultPrefixLookups() {
         final EnumSet<DefaultLookups> excluded = EnumSet.of(
                 DefaultLookups.DNS,
                 DefaultLookups.URL,
                 DefaultLookups.SCRIPT);
 
         final EnumSet<DefaultLookups> included = EnumSet.complementOf(excluded);
 
         final Map<String, Lookup> lookups = ConfigurationInterpolator.getDefaultPrefixLookups();
 
         assertEquals(included.size(), lookups.size());
         for (final DefaultLookups l : included) {
             assertSame(l.getLookup(), lookups.get(l.getPrefix()), "Wrong entry for " + l);
         }
 
         for (final DefaultLookups l : excluded) {
             assertNull(lookups.get(l.getPrefix()), "Unexpected entry for " + l);
         }
     }
 
     /**
      * Tests that the map with default lookups cannot be modified.
      */
     @Test
     void testGetDefaultPrefixLookupsModify() {
         final Map<String, Lookup> lookups = ConfigurationInterpolator.getDefaultPrefixLookups();
         final Lookup lookup = mock(Lookup.class);
         assertThrows(UnsupportedOperationException.class, () -> lookups.put("test", lookup));
 
         verifyNoInteractions(lookup);
     }
 
     /**
      * Tests that modification of the map with lookups does not affect the object.
      */
     @Test
     void testGetLookupsModify() {
         final Map<String, Lookup> lookups = interpolator.getLookups();
         lookups.put(TEST_PREFIX, setUpTestLookup());
         assertTrue(interpolator.getLookups().isEmpty());
     }
 
     /**
      * Tests creating an instance. Does it contain some predefined lookups and a default string converter?
      */
     @Test
     void testInit() {
         assertTrue(interpolator.getDefaultLookups().isEmpty());
         assertTrue(interpolator.getLookups().isEmpty());
         assertNull(interpolator.getParentInterpolator());
         assertNotNull(interpolator.getStringConverter());
         assertEquals("1", interpolator.getStringConverter().apply(Arrays.asList(1, 2)));
     }
 
     /**
      * Tests interpolation of an array argument.
      */
     @Test
     void testInterpolateArray() {
         final int[] value = {1, 2};
         assertSame(value, interpolator.interpolate(value));
     }
 
     /**
      * Tests that a blank variable definition does not cause problems.
      */
     @Test
     void testInterpolateBlankVariable() {
         final String value = "${ }";
         assertEquals(value, interpolator.interpolate(value));
     }
 
     /**
      * Tests interpolation of a collection argument.
      */
     @Test
     void testInterpolateCollection() {
         final List<Integer> value = Arrays.asList(1, 2);
         assertSame(value, interpolator.interpolate(value));
     }
 
     /**
      * Tests that an empty variable definition does not cause problems.
      */
     @Test
     void testInterpolateEmptyVariable() {
         final String value = "${}";
         assertEquals(value, interpolator.interpolate(value));
     }
 
     /**
      * Tests interpolation of a non string argument.
      */
     @Test
     void testInterpolateObject() {
         final Object value = 42;
         assertSame(value, interpolator.interpolate(value));
     }
 
     /**
      * Tests a successful interpolation of a string value.
      */
     @Test
     void testInterpolateString() {
         final String value = "${" + TEST_PREFIX + ':' + TEST_NAME + "}";
         interpolator.registerLookup(TEST_PREFIX, setUpTestLookup());
         assertEquals(TEST_VALUE, interpolator.interpolate(value));
     }
 
     /**
      * Tests interpolation with a variable which cannot be resolved.
      */
     @Test
     void testInterpolateStringUnknownVariable() {
         final String value = "${unknownVariable}";
         assertEquals(value, interpolator.interpolate(value));
     }
 
     /**
      * Tests an interpolated string that begins and ends with variable lookups that have
      * the potential to fail. Part of CONFIGURATION-764.
      */
     @Test
     void testInterpolationBeginningAndEndingRiskyVariableLookups() {
         interpolator.registerLookups(ConfigurationInterpolator.getDefaultPrefixLookups());
         final String result = (String) interpolator.interpolate("${date:yyyy-MM}-${date:dd}");
         assertTrue(result.matches("\\d{4}-\\d{2}-\\d{2}"));
     }
 
     /**
      * Tests interpolation with multiple variables containing arrays.
      */
     @Test
     void testInterpolationMultipleArrayVariables() {
         final String value = "${single}bc${multi}23${empty}${null}";
         final int[] multi = {1, 0, 0};
         final String[] single = {"a"};
         final int[] empty = {};
         final Object[] containsNull = {null};
         interpolator.addDefaultLookup(setUpTestLookup("multi", multi));
         interpolator.addDefaultLookup(setUpTestLookup("single", single));
         interpolator.addDefaultLookup(setUpTestLookup("empty", empty));
         interpolator.addDefaultLookup(setUpTestLookup("null", containsNull));
         assertEquals("abc123${empty}${null}", interpolator.interpolate(value));
     }
 
     /**
      * Tests interpolation with multiple variables containing collections and iterators.
      */
     @Test
     void testInterpolationMultipleCollectionVariables() {
         final String value = "${single}bc${multi}23${empty}${null}${multiIt}${emptyIt}${nullIt}";
         final List<Integer> multi = Arrays.asList(1, 0, 0);
         final List<String> single = Arrays.asList("a");
         final List<Object> empty = Collections.emptyList();
         final List<Object> containsNull = Arrays.asList((Object) null);
         interpolator.addDefaultLookup(setUpTestLookup("multi", multi));
         interpolator.addDefaultLookup(setUpTestLookup("multiIt", multi.iterator()));
         interpolator.addDefaultLookup(setUpTestLookup("single", single));
         interpolator.addDefaultLookup(setUpTestLookup("empty", empty));
         interpolator.addDefaultLookup(setUpTestLookup("emptyIt", empty.iterator()));
         interpolator.addDefaultLookup(setUpTestLookup("null", containsNull));
         interpolator.addDefaultLookup(setUpTestLookup("nullIt", containsNull.iterator()));
         assertEquals("abc123${empty}${null}1${emptyIt}${nullIt}", interpolator.interpolate(value));
     }
 
     /**
      * Tests interpolation with variables containing multiple simple non-string variables.
      */
     @Test
     void testInterpolationMultipleSimpleNonStringVariables() {
         final String value = "${x} = ${y} is ${result}";
         interpolator.addDefaultLookup(setUpTestLookup("x", 1));
         interpolator.addDefaultLookup(setUpTestLookup("y", 2));
         interpolator.addDefaultLookup(setUpTestLookup("result", false));
         assertEquals("1 = 2 is false", interpolator.interpolate(value));
     }
 
     /**
      * Tests a property value consisting of multiple variables.
      */
     @Test
     void testInterpolationMultipleVariables() {
         final String value = "The ${subject} jumps over ${object}.";
         interpolator.addDefaultLookup(setUpTestLookup("subject", "quick brown fox"));
         interpolator.addDefaultLookup(setUpTestLookup("object", "the lazy dog"));
         assertEquals("The quick brown fox jumps over the lazy dog.", interpolator.interpolate(value));
     }
 
     /**
      * Tests an interpolation that consists of a single array variable only. The variable's value
      * should be returned verbatim.
      */
     @Test
     void testInterpolationSingleArrayVariable() {
         final int[] value = {42, -1};
         interpolator.addDefaultLookup(setUpTestLookup(TEST_NAME, value));
         assertEquals(value, interpolator.interpolate("${" + TEST_NAME + "}"));
     }
 
     /**
      * Tests an interpolation that consists of a single collection variable only. The variable's value
      * should be returned verbatim.
      */
     @Test
     void testInterpolationSingleCollectionVariable() {
         final List<Integer> value = Arrays.asList(42);
         interpolator.addDefaultLookup(setUpTestLookup(TEST_NAME, value));
         assertEquals(value, interpolator.interpolate("${" + TEST_NAME + "}"));
     }
 
     /**
      * Tests an interpolation that consists of a single variable only. The variable's value should be returned verbatim.
      */
     @Test
     void testInterpolationSingleVariable() {
         final Object value = 42;
         interpolator.addDefaultLookup(setUpTestLookup(TEST_NAME, value));
         assertEquals(value, interpolator.interpolate("${" + TEST_NAME + "}"));
     }
 
     /**
      * Tests an interpolation that consists of a single undefined variable only with and without a default value.
      */
     @Test
     void testInterpolationSingleVariableDefaultValue() {
         final Object value = 42;
         interpolator.addDefaultLookup(setUpTestLookup(TEST_NAME, value));
         assertEquals("${I_am_not_defined}", interpolator.interpolate("${I_am_not_defined}"));
         assertEquals("42", interpolator.interpolate("${I_am_not_defined:-42}"));
         assertEquals("", interpolator.interpolate("${I_am_not_defined:-}"));
     }
 
     /**
      * Tests a variable declaration which lacks the trailing closing bracket.
      */
     @Test
     void testInterpolationVariableIncomplete() {
         final String value = "${" + TEST_NAME;
         interpolator.addDefaultLookup(setUpTestLookup(TEST_NAME, "someValue"));
         assertEquals(value, interpolator.interpolate(value));
     }
 
     /**
      * Tests nullSafeLookup() if a lookup object was provided.
      */
     @Test
     void testNullSafeLookupExisting() {
         final Lookup look = mock(Lookup.class);
         assertSame(look, ConfigurationInterpolator.nullSafeLookup(look));
     }
 
     /**
      * Tests whether nullSafeLookup() can handle null input.
      */
     @Test
     void testNullSafeLookupNull() {
         final Lookup lookup = ConfigurationInterpolator.nullSafeLookup(null);
         assertNull(lookup.lookup("someVar"));
     }
 
     /**
      * Tests that the prefix set cannot be modified.
      */
     @Test
     void testPrefixSetModify() {
         interpolator.registerLookup(TEST_PREFIX, setUpTestLookup());
         final Iterator<String> it = interpolator.prefixSet().iterator();
         it.next();
         assertThrows(UnsupportedOperationException.class, it::remove);
     }
 
     /**
      * Tests registering a lookup object at an instance.
      */
     @Test
     void testRegisterLookup() {
         final Lookup lookup = mock(Lookup.class);
         interpolator.registerLookup(TEST_PREFIX, lookup);
         assertSame(lookup, interpolator.getLookups().get(TEST_PREFIX));
         assertTrue(interpolator.prefixSet().contains(TEST_PREFIX));
         assertTrue(interpolator.getDefaultLookups().isEmpty());
     }
 
     /**
      * Tests registering a null lookup object. This should cause an exception.
      */
     @Test
     void testRegisterLookupNull() {
         assertThrows(IllegalArgumentException.class, () -> interpolator.registerLookup(TEST_PREFIX, null));
     }
 
     /**
      * Tests registering a lookup object for an undefined prefix. This should cause an exception.
      */
     @Test
     void testRegisterLookupNullPrefix() {
         final Lookup lookup = mock(Lookup.class);
         assertThrows(IllegalArgumentException.class, () -> interpolator.registerLookup(null, lookup));
 
         verifyNoInteractions(lookup);
     }
 
     /**
      * Tests whether a map with lookup objects can be registered.
      */
     @Test
     void testRegisterLookups() {
         final Lookup l1 = setUpTestLookup();
         final Lookup l2 = setUpTestLookup("someVar", "someValue");
         final Map<String, Lookup> lookups = new HashMap<>();
         lookups.put(TEST_PREFIX, l1);
         final String prefix2 = TEST_PREFIX + "_other";
         lookups.put(prefix2, l2);
         interpolator.registerLookups(lookups);
         final Map<String, Lookup> lookups2 = interpolator.getLookups();
 
         final Map<String, Lookup> expected = new HashMap<>();
         expected.put(TEST_PREFIX, l1);
         expected.put(prefix2, l2);
         assertEquals(expected, lookups2);
     }
 
     /**
      * Tests whether a null map with lookup objects is handled correctly.
      */
     @Test
     void testRegisterLookupsNull() {
         interpolator.registerLookups(null);
         assertTrue(interpolator.getLookups().isEmpty());
     }
 
     /**
      * Tests whether a default lookup object can be removed.
      */
     @Test
     void testRemoveDefaultLookup() {
         final List<Lookup> lookups = new ArrayList<>();
         lookups.add(setUpTestLookup());
         lookups.add(setUpTestLookup("test", "value"));
         interpolator.addDefaultLookups(lookups);
         assertTrue(interpolator.removeDefaultLookup(lookups.get(0)));
         assertFalse(interpolator.getDefaultLookups().contains(lookups.get(0)));
         assertEquals(1, interpolator.getDefaultLookups().size());
     }
 
     /**
      * Tests whether a non existing default lookup object can be removed.
      */
     @Test
     void testRemoveDefaultLookupNonExisting() {
         assertFalse(interpolator.removeDefaultLookup(setUpTestLookup()));
     }
 
     /**
      * Tests looking up a variable without a prefix. This should trigger the default lookup object.
      */
     @Test
     void testResolveDefault() {
         final Lookup l1 = mock(Lookup.class);
         final Lookup l2 = mock(Lookup.class);
         final Lookup l3 = mock(Lookup.class);
 
         when(l1.lookup(TEST_NAME)).thenReturn(null);
         when(l2.lookup(TEST_NAME)).thenReturn(TEST_VALUE);
 
         interpolator.addDefaultLookups(Arrays.asList(l1, l2, l3));
         assertEquals(TEST_VALUE, interpolator.resolve(TEST_NAME));
 
         verify(l1).lookup(TEST_NAME);
         verify(l2).lookup(TEST_NAME);
         verifyNoMoreInteractions(l1, l2, l3);
     }
 
     /**
      * Tests whether the default lookup is called for variables with a prefix when the lookup that was registered for this
      * prefix is not able to resolve the variable.
      */
     @Test
     void testResolveDefaultAfterPrefixFails() {
         final String varName = TEST_PREFIX + ':' + TEST_NAME + "2";
         interpolator.registerLookup(TEST_PREFIX, setUpTestLookup());
         interpolator.addDefaultLookup(setUpTestLookup(varName, TEST_VALUE));
         assertEquals(TEST_VALUE, interpolator.resolve(varName));
     }
 
     /**
      * Tests an empty variable name without a prefix.
      */
     @Test
     void testResolveDefaultEmptyVarName() {
         interpolator.addDefaultLookup(setUpTestLookup("", TEST_VALUE));
         assertEquals(TEST_VALUE, interpolator.resolve(""));
     }
 
     /**
      * Tests the empty variable prefix. This is a special case, but legal.
      */
     @Test
     void testResolveEmptyPrefix() {
         interpolator.registerLookup("", setUpTestLookup());
         assertEquals(TEST_VALUE, interpolator.resolve(":" + TEST_NAME));
     }
 
     /**
      * Tests an empty variable name.
      */
     @Test
     void testResolveEmptyVarName() {
         interpolator.registerLookup(TEST_PREFIX, setUpTestLookup("", TEST_VALUE));
         assertEquals(TEST_VALUE, interpolator.resolve(TEST_PREFIX + ":"));
     }
 
     /**
      * Tests looking up a variable without a prefix when no default lookup is specified. Result should be null in this case.
      */
     @Test
     void testResolveNoDefault() {
         assertNull(interpolator.resolve(TEST_NAME));
     }
 
     /**
      * Tests looking up a null variable. Result should be null, too.
      */
     @Test
     void testResolveNull() {
         assertNull(interpolator.resolve(null));
     }
 
     /**
      * Tests handling of a parent {@code ConfigurationInterpolator} if the variable can already be resolved by the current
      * instance.
      */
     @Test
     void testResolveParentVariableFound() {
         final ConfigurationInterpolator parent = mock(ConfigurationInterpolator.class);
         interpolator.setParentInterpolator(parent);
         interpolator.registerLookup(TEST_PREFIX, setUpTestLookup());
         assertEquals(TEST_VALUE, interpolator.resolve(TEST_PREFIX + ':' + TEST_NAME));
     }
 
     /**
      * Tests whether the parent {@code ConfigurationInterpolator} is invoked if the test instance cannot resolve a variable.
      */
     @Test
     void testResolveParentVariableNotFound() {
         final ConfigurationInterpolator parent = mock(ConfigurationInterpolator.class);
 
         when(parent.resolve(TEST_NAME)).thenReturn(TEST_VALUE);
 
         interpolator.setParentInterpolator(parent);
         assertEquals(TEST_VALUE, interpolator.resolve(TEST_NAME));
 
         verify(parent).resolve(TEST_NAME);
         verifyNoMoreInteractions(parent);
     }
 
     /**
      * Tests whether a variable can be resolved using the associated lookup object. The lookup is identified by the
      * variable's prefix.
      */
     @Test
     void testResolveWithPrefix() {
         interpolator.registerLookup(TEST_PREFIX, setUpTestLookup());
         assertEquals(TEST_VALUE, interpolator.resolve(TEST_PREFIX + ':' + TEST_NAME));
     }
 
     /**
      * Tests the behavior of the lookup method for variables with an unknown prefix. These variables should not be resolved.
      */
     @Test
     void testResolveWithUnknownPrefix() {
         interpolator.registerLookup(TEST_PREFIX, setUpTestLookup());
         assertNull(interpolator.resolve("UnknownPrefix:" + TEST_NAME));
         assertNull(interpolator.resolve(":" + TEST_NAME));
     }
 
     /**
      * Tests that a custom string converter can be used.
      */
     @Test
     void testSetStringConverter() {
         final Function<Object, String> stringConverter = obj -> "'" + obj + "'";
         interpolator.addDefaultLookup(setUpTestLookup("x", Arrays.asList(1, 2)));
         interpolator.addDefaultLookup(setUpTestLookup("y", "abc"));
         interpolator.setStringConverter(stringConverter);
         assertSame(stringConverter, interpolator.getStringConverter());
         assertEquals("'abc': '[1, 2]'", interpolator.interpolate("${y}: ${x}"));
     }
 
     /**
      * Tests that the default string converter can be reapplied by passing {@code null}.
      */
     @Test
     void testSetStringConverterNullArgumentUsesDefault() {
         final Function<Object, String> stringConverter = obj -> "'" + obj + "'";
         interpolator.addDefaultLookup(setUpTestLookup("x", Arrays.asList(1, 2)));
         interpolator.addDefaultLookup(setUpTestLookup("y", "abc"));
         interpolator.setStringConverter(stringConverter);
         interpolator.setStringConverter(null);
         assertNotSame(stringConverter, interpolator.getStringConverter());
         assertEquals("abc: 1", interpolator.interpolate("${y}: ${x}"));
     }
 }