Additional unit tests for operations on empty UriTemplate

See gh-32432

(cherry picked from commit 54a6d89da7)

spring-web/src/test/java/org/springframework/web/util/UriTemplateTests.java

@@ -53,6 +53,13 @@ class UriTemplateTests {
 		assertThat(variableNames).as("Invalid variable names").isEqualTo(Arrays.asList("hotel", "booking"));
 	}
 
+	@Test
+	void getVariableNamesFromEmpty() {
+		UriTemplate template = new UriTemplate("");
+		List<String> variableNames = template.getVariableNames();
+		assertThat(variableNames).isEmpty();
+	}
+
 	@Test
 	void expandVarArgs() {
 		UriTemplate template = new UriTemplate("/hotels/{hotel}/bookings/{booking}");
@@ -60,6 +67,13 @@ class UriTemplateTests {
 		assertThat(result).as("Invalid expanded template").isEqualTo(URI.create("/hotels/1/bookings/42"));
 	}
 
+	@Test
+	void expandVarArgsFromEmpty() {
+		UriTemplate template = new UriTemplate("");
+		URI result = template.expand();
+		assertThat(result).as("Invalid expanded template").isEqualTo(URI.create(""));
+	}
+
 	@Test  // SPR-9712
 	void expandVarArgsWithArrayValue() {
 		UriTemplate template = new UriTemplate("/sum?numbers={numbers}");
@@ -135,6 +149,15 @@ class UriTemplateTests {
 		assertThat(template.matches(null)).as("UriTemplate matches").isFalse();
 	}
 
+	@Test
+	void matchesAgainstEmpty() {
+		UriTemplate template = new UriTemplate("");
+		assertThat(template.matches("/hotels/1/bookings/42")).as("UriTemplate matches").isFalse();
+		assertThat(template.matches("/hotels/bookings")).as("UriTemplate matches").isFalse();
+		assertThat(template.matches("")).as("UriTemplate does not match").isTrue();
+		assertThat(template.matches(null)).as("UriTemplate matches").isFalse();
+	}
+
 	@Test
 	void matchesCustomRegex() {
 		UriTemplate template = new UriTemplate("/hotels/{hotel:\\d+}");
@@ -153,6 +176,13 @@ class UriTemplateTests {
 		assertThat(result).as("Invalid match").isEqualTo(expected);
 	}
 
+	@Test
+	void matchAgainstEmpty() {
+		UriTemplate template = new UriTemplate("");
+		Map<String, String> result = template.match("/hotels/1/bookings/42");
+		assertThat(result).as("Invalid match").isEmpty();
+	}
+
 	@Test
 	void matchCustomRegex() {
 		Map<String, String> expected = new HashMap<>(2);