Polish "Add support for converting String to Pattern"

See gh-24311

spring-core/src/test/java/org/springframework/core/convert/converter/DefaultConversionServiceTests.java

@@ -319,10 +319,16 @@ class DefaultConversionServiceTests {
 		assertThat(convertToUUID).isEqualTo(uuid);
 	}
 
+	@Test
+	void stringToPatternEmptyString() {
+		assertThat(conversionService.convert("", Pattern.class)).isNull();
+	}
+
 	@Test
 	void stringToPattern() {
-		String regex = "\\s";
-		assertThat(conversionService.convert(regex, Pattern.class)).extracting(Pattern::pattern).isEqualTo(regex);
+		String pattern = "\\s";
+		assertThat(conversionService.convert(pattern, Pattern.class))
+				.isInstanceOfSatisfying(Pattern.class, regex -> assertThat(regex.pattern()).isEqualTo(pattern));
 	}
 
 	@Test

spring-core/src/test/kotlin/org/springframework/core/convert/support/DefaultConversionServiceKotlinTests.kt

@@ -0,0 +1,34 @@
+package org.springframework.core.convert.support
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+/**
+ * Tests for Kotlin support in [DefaultConversionService].
+ *
+ * @author Stephane Nicoll
+ */
+class DefaultConversionServiceKotlinTests {
+
+	private val conversionService = DefaultConversionService()
+
+	@Test
+	fun stringToRegexEmptyString() {
+		assertThat(conversionService.convert("", Regex::class.java)).isNull();
+	}
+
+	@Test
+	fun stringToRegex() {
+		val pattern = "\\w+"
+		assertThat(conversionService.convert(pattern, Regex::class.java)).isInstanceOfSatisfying(
+			Regex::class.java
+		) { regex -> assertThat(regex.pattern).isEqualTo(pattern) }
+	}
+
+	@Test
+	fun regexToString() {
+		val pattern = "\\w+"
+		assertThat(conversionService.convert(pattern.toRegex(), String::class.java)).isEqualTo(pattern)
+	}
+
+}