diff --git a/src/test/java/com/tabs/utility/PlanConfigTest.java b/src/test/java/com/tabs/utility/PlanConfigTest.java
new file mode 100644
index 0000000..ccf452c
--- /dev/null
+++ b/src/test/java/com/tabs/utility/PlanConfigTest.java
@@ -0,0 +1,128 @@
+package com.tabs.utility;
+
+import com.tabs.models.Plan;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class PlanConfigTest {
+
+    @Test
+    void getPlanById_returnsSystemPlanForKnownId() {
+        Plan plan = PlanConfig.getPlanById("UNIV-01");
+
+        assertNotNull(plan);
+        assertSame(PlanConfig.SYSTEM_PLAN, plan);
+        assertEquals("UNIV-01", plan.getPlanId());
+        assertEquals("Universal Plan 799", plan.getPlanName());
+        assertEquals(799.0, plan.getMonthlyRental());
+        assertEquals(100.0, plan.getVoiceAllowedMins());
+        assertEquals(5000.0, plan.getDataAllowanceGB());
+        assertEquals(100, plan.getSmsAllowed());
+        assertEquals(9.0, plan.getVoiceOverageRatePerMin());
+        assertEquals(0.9, plan.getDataOverageRatePerGB());
+        assertEquals(0.5, plan.getSmsOveragePerSMS());
+        assertEquals(500.0, plan.getWeekendFreeMinutes());
+        assertTrue(plan.isFamilyShared());
+    }
+
+    @Test
+    void getPlanById_returnsLitePlanForKnownId() {
+        Plan plan = PlanConfig.getPlanById("LITE-01");
+
+        assertNotNull(plan);
+        assertSame(PlanConfig.SYSTEM_PLAN_LITE, plan);
+        assertEquals("LITE-01", plan.getPlanId());
+        assertEquals("Lite Plan 599", plan.getPlanName());
+        assertEquals(599.0, plan.getMonthlyRental());
+        assertEquals(70.0, plan.getVoiceAllowedMins());
+        assertEquals(3000.0, plan.getDataAllowanceGB());
+        assertEquals(50, plan.getSmsAllowed());
+        assertEquals(9.0, plan.getVoiceOverageRatePerMin());
+        assertEquals(0.9, plan.getDataOverageRatePerGB());
+        assertEquals(0.5, plan.getSmsOveragePerSMS());
+        assertEquals(500.0, plan.getWeekendFreeMinutes());
+        assertTrue(plan.isFamilyShared());
+    }
+
+    @Test
+    void getPlanById_isCaseSensitiveAndRejectsMalformedKeys() {
+        assertNull(PlanConfig.getPlanById("univ-01"));
+        assertNull(PlanConfig.getPlanById("UNIV-01 "));
+        assertNull(PlanConfig.getPlanById(" UNIV-01"));
+        assertNull(PlanConfig.getPlanById("UNIV_01"));
+        assertNull(PlanConfig.getPlanById(""));
+        assertNull(PlanConfig.getPlanById("   "));
+        assertNull(PlanConfig.getPlanById("LITE-1"));
+        assertNull(PlanConfig.getPlanById("LITE-01-extra"));
+    }
+
+    @Test
+    void getPlanById_returnsNullForMissingOrNullPlanId() {
+        assertNull(PlanConfig.getPlanById("MISSING-PLAN"));
+        assertNull(PlanConfig.getPlanById(null));
+    }
+
+    @Test
+    void systemPlansAreRegisteredAndRemainDistinct() {
+        assertNotNull(PlanConfig.SYSTEM_PLAN);
+        assertNotNull(PlanConfig.SYSTEM_PLAN_LITE);
+        assertNotSame(PlanConfig.SYSTEM_PLAN, PlanConfig.SYSTEM_PLAN_LITE);
+        assertEquals("UNIV-01", PlanConfig.SYSTEM_PLAN.getPlanId());
+        assertEquals("LITE-01", PlanConfig.SYSTEM_PLAN_LITE.getPlanId());
+        assertNotEquals(PlanConfig.SYSTEM_PLAN.getMonthlyRental(), PlanConfig.SYSTEM_PLAN_LITE.getMonthlyRental());
+    }
+
+    @Test
+    void planDefaultConstructorSetsFamilySharedFalseAndSettersExposeProperties() {
+        Plan plan = new Plan();
+
+        assertFalse(plan.isFamilyShared());
+        assertNull(plan.getPlanId());
+        assertNull(plan.getPlanName());
+        assertNull(plan.getMonthlyRental());
+        assertNull(plan.getDataAllowanceGB());
+        assertNull(plan.getVoiceAllowedMins());
+        assertNull(plan.getSmsAllowed());
+        assertNull(plan.getDataOverageRatePerGB());
+        assertNull(plan.getVoiceOverageRatePerMin());
+        assertNull(plan.getSmsOveragePerSMS());
+        assertNull(plan.getWeekendFreeMinutes());
+
+        plan.setPlanId("TEST-01");
+        plan.setPlanName("Test Plan");
+        plan.setMonthlyRental(123.45);
+        plan.setDataAllowanceGB(10.0);
+        plan.setVoiceAllowedMins(20.0);
+        plan.setSmsAllowed(30);
+        plan.setDataOverageRatePerGB(1.1);
+        plan.setVoiceOverageRatePerMin(2.2);
+        plan.setSmsOveragePerSMS(3.3);
+        plan.setWeekendFreeMinutes(40.0);
+        plan.setFamilyShared(true);
+
+        assertEquals("TEST-01", plan.getPlanId());
+        assertEquals("Test Plan", plan.getPlanName());
+        assertEquals(123.45, plan.getMonthlyRental());
+        assertEquals(10.0, plan.getDataAllowanceGB());
+        assertEquals(20.0, plan.getVoiceAllowedMins());
+        assertEquals(30, plan.getSmsAllowed());
+        assertEquals(1.1, plan.getDataOverageRatePerGB());
+        assertEquals(2.2, plan.getVoiceOverageRatePerMin());
+        assertEquals(3.3, plan.getSmsOveragePerSMS());
+        assertEquals(40.0, plan.getWeekendFreeMinutes());
+        assertTrue(plan.isFamilyShared());
+    }
+
+    @Test
+    void planConstantsHaveExpectedValues() {
+        assertEquals(0.18, PlanConfig.GST_RATE);
+        assertEquals(0.05, PlanConfig.REFERRAL_DISCOUNT_RATE);
+        assertEquals(0.5, PlanConfig.NIGHT_TIME_DATA_DISCOUNT_WEIGHT);
+        assertEquals(0.15, PlanConfig.DOMESTIC_ROAMING_SURCHARGE_RATE);
+        assertEquals(0.60, PlanConfig.FAMILY_FAIRNESS_USAGE_THRESHOLD);
+        assertEquals(250.0, PlanConfig.FAMILY_FAIRNESS_SURCHARGE);
+        assertEquals(0.50, PlanConfig.DATA_ROLLOVER_CAP_PERCENT);
+        assertEquals(60, PlanConfig.CREDIT_CONTROL_DAYS_THRESHOLD);
+    }
+}