[KTLN-809] Add Samples (#826)

Author: LeoColman

core-kotlin-modules/core-kotlin-numbers/src/main/kotlin/com/baeldung/percentage/Percentage.kt

@@ -0,0 +1,21 @@
+package com.baeldung.percentage
+
+import java.math.BigDecimal
+import java.math.RoundingMode
+
+fun Number.divideToPercent(divideTo: Number): Double {
+    if (divideTo.toDouble() == 0.0) return 0.0
+    return (this.toDouble() / divideTo.toDouble()) * 100.0
+}
+
+infix fun Number.percentOf(value: Number): Double {
+    return if (this.toDouble() == 0.0) 0.0
+    else (value.toDouble() / this.toDouble())
+}
+
+fun BigDecimal.percentOf(total: BigDecimal): BigDecimal {
+    return if (total == BigDecimal.ZERO) BigDecimal.ZERO
+    else this.divide(total, 5, RoundingMode.HALF_UP) * BigDecimal(100)
+}
+
+fun Number.formatPercent() = "$this%"

core-kotlin-modules/core-kotlin-numbers/src/test/kotlin/com/baeldung/percentage/CalculatePercentageUnitTest.kt

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+package com.baeldung.percentage
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+import java.math.BigDecimal
+
+class CalculatePercentageUnitTest {
+    @Test
+    fun `should return accurate division result`() {
+        val count = 5
+        val totalCount = 10
+        val expected = 50.0
+        val result = (count.toDouble() / totalCount.toDouble()) * 100.0
+        assertEquals(expected, result)
+    }
+
+    @Test
+    fun `when dividing 10 by 20, should return 50`() {
+        val result = 10.divideToPercent(20)
+        assertEquals(50.0, result)
+    }
+
+    @Test
+    fun `when using infix function, 10 percentOf 200 should return 20`() {
+        val result = 10 percentOf 200
+        assertEquals(20.0, result)
+    }
+
+    @Test fun `calculate percentage using BigDecimal for high precision`() {
+        val part = BigDecimal("25")
+        val whole = BigDecimal("200")
+        val expectedPercentage = BigDecimal("12.50") // Expecting 12.50% as the result
+        val resultPercentage = part.percentOf(whole)
+        assertTrue { resultPercentage.compareTo(expectedPercentage) == 0 }
+    }
+}