Add testing for the IntFormat (found a bug!)

selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/Literals.kt

@@ -30,7 +30,7 @@ class IntFormat : LiteralFormat<Int> {
     return value.toString()
   }
   override fun parse(str: String): Int {
-    return str.toInt()
+    return str.replace("_", "").toInt()
   }
 }
 

selfie-lib/src/commonTest/kotlin/com/diffplug/selfie/IntFormatTest.kt

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2023 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.selfie
+
+import io.kotest.matchers.shouldBe
+import kotlin.test.Test
+
+class IntFormatTest {
+  @Test
+  fun encode() {
+    encode(0, "0")
+    encode(1, "1")
+    encode(-1, "-1")
+    encode(999, "999")
+    encode(-999, "-999")
+    // TODO: add underscores
+    encode(1_000, "1000")
+    encode(-1_000, "-1000")
+    encode(1_000_000, "1000000")
+    encode(-1_000_000, "-1000000")
+  }
+  private fun encode(value: Int, expected: String) {
+    val actual = IntFormat().encode(value)
+    actual shouldBe expected
+  }
+
+  @Test
+  fun decode() {
+    decode("0", 0)
+    decode("1", 1)
+    decode("-1", -1)
+    decode("999", 999)
+    decode("9_99", 999)
+    decode("9_9_9", 999)
+    decode("-999", -999)
+    decode("-9_99", -999)
+    decode("-9_9_9", -999)
+  }
+  private fun decode(value: String, expected: Int) {
+    val actual = IntFormat().parse(value)
+    actual shouldBe expected
+  }
+}