test: improve coverage for DiscreteLogarithmBSGS

Author: rajucreate

src/test/java/com/thealgorithms/maths/DiscreteLogarithmBSGSTest.java

@@ -25,4 +25,18 @@ public void testLargeMod() {
         long x = DiscreteLogarithmBSGS.discreteLog(5, 5, 1000003);
         assertEquals(1, x);
     }
+
+    @Test
+    public void testImmediateReturnCase() {
+        // because a^0 ≡ 1 (mod m)
+        assertEquals(0, DiscreteLogarithmBSGS.discreteLog(7, 1, 13));
+    }
+
+    @Test
+    public void testModPowBranchCoverage() {
+        assertEquals(1, DiscreteLogarithmBSGS.modPow(10, 0, 17)); // exp=0 branch
+        assertEquals(10 % 17, DiscreteLogarithmBSGS.modPow(10, 1, 17)); // odd exp branch
+        assertEquals(100 % 17, DiscreteLogarithmBSGS.modPow(10, 2, 17)); // even exp branch
+    }
+
 }