test: add edge test cases for add and remove methods in SortedSet

Author: Md-Talim

src/test/java/redis/store/SortedSetTest.java

@@ -21,6 +21,12 @@ void addReturnsTrueForNewMember() {
 
     @Test
     void addReturnsFalseForExistingMember() {
+        assertThat(set.add("alice", 1.0)).isTrue();
+        assertThat(set.add("alice", 1.0)).isFalse();
+    }
+
+    @Test
+    void addReturnsFalseWhenUpdatingExistingMemberScore() {
         set.add("alice", 1.0);
         assertThat(set.add("alice", 2.0)).isFalse();
     }
@@ -57,6 +63,11 @@ void removeDeletesMember() {
         assertThat(set.size()).isEqualTo(0);
     }
 
+    @Test
+    void removeMissingMemberReturnsFalse() {
+        assertThat(set.remove("nonexistent")).isFalse();
+    }
+
     @Test
     void getScoreReturnsCorrectValue() {
         set.add("alice", 42.5);