Added unit test.

Author: javadev

src/test/kotlin/com_github_leetcode/NestedIntegerTest.kt

@@ -0,0 +1,38 @@
+package com_github_leetcode
+
+import org.hamcrest.CoreMatchers
+import org.hamcrest.MatcherAssert
+import org.junit.jupiter.api.Test
+
+internal class NestedIntegerTest {
+    @Test
+    fun constructor() {
+        val nestedInteger = NestedInteger()
+        MatcherAssert.assertThat(nestedInteger.getInteger(), CoreMatchers.equalTo(null))
+        MatcherAssert.assertThat(nestedInteger.isInteger(), CoreMatchers.equalTo(false))
+    }
+
+    @Test
+    fun constructor2() {
+        val list = mutableListOf(NestedInteger())
+        val nestedInteger = NestedInteger(list)
+        MatcherAssert.assertThat(nestedInteger.getInteger(), CoreMatchers.equalTo(null))
+        MatcherAssert.assertThat(nestedInteger.getList(), CoreMatchers.equalTo(list))
+    }
+
+    @Test
+    fun constructor3() {
+        val nestedInteger = NestedInteger(1)
+        MatcherAssert.assertThat(nestedInteger.getInteger(), CoreMatchers.equalTo(1))
+        MatcherAssert.assertThat(nestedInteger.isInteger(), CoreMatchers.equalTo(true))
+    }
+
+    @Test
+    fun add() {
+        val nestedInteger = NestedInteger(ArrayList(listOf(NestedInteger(1))))
+        nestedInteger.add(NestedInteger(2))
+        MatcherAssert.assertThat(nestedInteger.getList()!!.size, CoreMatchers.equalTo(2))
+        MatcherAssert.assertThat(nestedInteger.getList()!![0].getInteger(), CoreMatchers.equalTo(1))
+        MatcherAssert.assertThat(nestedInteger.getList()!![1].getInteger(), CoreMatchers.equalTo(2))
+    }
+}