@@ -0,0 +1,101 @@
+package nextstep.security.role;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.NullAndEmptySource;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.util.Collection;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class RoleHierarchyImplTest {
+
+    RoleHierarchyImpl.Builder builder;
+
+    @BeforeEach
+    void setUp() {
+        builder = RoleHierarchyImpl.builder()
+                .role("ADMIN").addImplies("MEMBER");
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"ADMIN", "MEMBER", "UNKNOWN"})
+    @DisplayName("역할 계층을 Authority 로 가져올 수 있다")
+    void getRoleHierarchyTest(String roleName) {
+        // given
+        RoleHierarchyImpl roleHierarchy = builder.build();
+
+        // when
+        SimpleGrantedAuthority authority = new SimpleGrantedAuthority(roleName);
+        Collection<GrantedAuthority> reachableRoles = roleHierarchy.getReachableRoles(List.of(authority));
+
+        // then
+        List<GrantedAuthority> expect = switch (roleName) {
+            case "ADMIN" -> List.of(
+                    new SimpleGrantedAuthority("ADMIN"),
+                    new SimpleGrantedAuthority("MEMBER")
+            );
+            case "MEMBER", "UNKNOWN" -> List.of(
+                    new SimpleGrantedAuthority(roleName)
+            );
+            default -> throw new IllegalStateException("Unexpected roleName: " + roleName);
+        };
+
+        assertThat(reachableRoles)
+                .containsExactlyInAnyOrderElementsOf(expect);
+    }
+
+    @Test
+    @DisplayName("새로운 역할 계층을 추가할 수 있다.")
+    void addRoleHierarchyTest() {
+        // given
+        String target = "ISRAEL";
+        String nothing = "NOTHING";
+        String everything = "EVERYTHING";
+        RoleHierarchyImpl roleHierarchy = builder.role(target).addImplies(nothing, everything)
+                .build();
+
+        // when
+        SimpleGrantedAuthority authority = new SimpleGrantedAuthority(target);
+        Collection<GrantedAuthority> reachableRoles = roleHierarchy.getReachableRoles(List.of(authority));
+
+        // then
+        var expect = List.of(
+                authority,
+                new SimpleGrantedAuthority(nothing),
+                new SimpleGrantedAuthority(everything)
+        );
+        assertThat(reachableRoles).hasSize(3)
+                .containsExactlyInAnyOrderElementsOf(expect);
+    }
+
+    @ParameterizedTest
+    @NullAndEmptySource
+    @DisplayName("역할의 이름은 비어있을수 없다")
+    void addRoleHierarchyFailTest1(String roleName) {
+        assertThatThrownBy(
+                () -> builder.role(roleName)
+        ).isInstanceOf(IllegalArgumentException.class)
+                .hasMessageContaining("role must not be null or empty");
+    }
+
+    @ParameterizedTest
+    @NullAndEmptySource
+    @DisplayName("포함된 역할들도 비어있을 수 없다.")
+    void addRoleHierarchyFailTest2(String roleName) {
+        // given
+        String target = "NEW_ROLE";
+        RoleHierarchyImpl.Builder.ImpliedRoles impliedRoles = builder.role(target);
+
+        // when
+        assertThatThrownBy(
+                () -> impliedRoles.addImplies(roleName)
+        ).isInstanceOf(IllegalArgumentException.class)
+                .hasMessageContaining("at least one implied role must be provided");
+    }
+}

리뷰: 그래서 추가함(`addImplies`)를 테스트하고싶다면 정말 값이 추가되었는지 그 자체만을 테스트하는 것이 나을 수도 있어요. `private final Map<String, Set<GrantedAuthority>> rolesReachableInOneOrMoreStepsMap;`에 원하는 값이 있는지 확인하는 것으로요.