chore(common-utils): Split tests into matching files

In 6d34ce5 the implementations were split across multiple files, but the
tests were forgotten. Make good for that now.

Signed-off-by: Sebastian Schuberth <[email protected]>

Author: sschuberth

utils/common/src/test/kotlin/EnumUtilsTest.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2017 The ORT Project Authors (see <https://github.com/oss-review-toolkit/ort/blob/main/NOTICE>)
+ *
+ * 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.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * License-Filename: LICENSE
+ */
+
+package org.ossreviewtoolkit.utils.common
+
+import io.kotest.core.spec.style.WordSpec
+import io.kotest.matchers.collections.beEmpty
+import io.kotest.matchers.should
+import io.kotest.matchers.shouldBe
+
+import java.time.DayOfWeek
+
+class EnumUtilsTest : WordSpec({
+    "The plus operator" should {
+        "create an empty set if both summands are empty" {
+            val sum = enumSetOf<DayOfWeek>() + enumSetOf()
+
+            sum should beEmpty()
+        }
+
+        "create the correct sum of two sets" {
+            val sum = enumSetOf(DayOfWeek.MONDAY, DayOfWeek.TUESDAY) + enumSetOf(DayOfWeek.TUESDAY, DayOfWeek.WEDNESDAY)
+
+            sum shouldBe enumSetOf(DayOfWeek.MONDAY, DayOfWeek.TUESDAY, DayOfWeek.WEDNESDAY)
+        }
+    }
+})