KTLN-832 Removing Ambiguity in Kotlin Function by Reference (#1186)

* added unit tests

* code changes

* code fixes

* code fixes

* code changes

* code changes

Author: albertache1998

Diff for: core-kotlin-modules/core-kotlin-advanced-4/src/test/kotlin/com/baeldung/removeAmbiguityInKotlinFunctionByReference/RemoveAmbiguityInKotlinFunctionByReferenceUnitTest.kt

@@ -0,0 +1,72 @@
+package com.baeldung.removeAmbiguityInKotlinFunctionByReference
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+
+typealias StringComputer = (String) -> String
+
+typealias IntComputer = (Int) -> Int
+
+class Calculator(val base: Int) {
+    fun compute(value: Int): Int = base + value
+    fun compute(value: String): String = "$base$value"
+}
+
+fun Calculator.computeInt(value: Int): Int = compute(value)
+
+fun Calculator.computeString(value: String): String = compute(value)
+
+class RemoveAmbiguityInKotlinFunctionByReferenceUnitTest {
+
+    private val calculator = Calculator(10)
+
+    @Test
+    fun `Should compute with int function`() {
+        val computeInt: (Int) -> Int = calculator::compute
+        assertEquals(15, computeInt(5))
+    }
+
+    @Test
+    fun `Should compute with string function`() {
+        val computeString: (String) -> String = calculator::compute
+        assertEquals("105", computeString("5"))
+    }
+
+    @Test
+    fun `Should compute int with lambda`() {
+        val computeInt = { value: Int -> calculator.compute(value) }
+        assertEquals(15, computeInt(5))
+    }
+
+    @Test
+    fun `Should compute string with lambda`() {
+        val computeString = { value: String -> calculator.compute(value) }
+        assertEquals("105", computeString("5"))
+    }
+
+    @Test
+    fun `should compute int with extension function`() {
+        val computeIntFn = calculator::computeInt
+        assertEquals(15, computeIntFn(5))
+    }
+
+    @Test
+    fun `should compute string with extension function`() {
+        val computeStringFn = calculator::computeString
+        assertEquals("105", computeStringFn("5"))
+    }
+
+
+    @Test
+    fun `Should compute int with type alias`() {
+        val computeInt: IntComputer = calculator::compute
+        assertEquals(15, computeInt(5))
+    }
+
+    @Test
+    fun `Should compute string with type alias`() {
+        val computeString: StringComputer = calculator::compute
+        assertEquals("105", computeString("5"))
+    }
+}