Added test coverage

src/test/groovy/net/fortuna/ical4j/validate/CalendarValidatorImplTest.groovy

@@ -0,0 +1,73 @@
+/*
+ *  Copyright (c) 2022, Ben Fortuna
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions
+ *  are met:
+ *
+ *   o Redistributions of source code must retain the above copyright
+ *  notice, this list of conditions and the following disclaimer.
+ *
+ *   o Redistributions in binary form must reproduce the above copyright
+ *  notice, this list of conditions and the following disclaimer in the
+ *  documentation and/or other materials provided with the distribution.
+ *
+ *   o Neither the name of Ben Fortuna nor the names of any other contributors
+ *  may be used to endorse or promote products derived from this software
+ *  without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ *  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ *  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ *  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ *  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ *  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ *  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ *  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ *  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ *  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+package net.fortuna.ical4j.validate
+
+import net.fortuna.ical4j.model.ContentBuilder
+import net.fortuna.ical4j.model.property.Attach
+import spock.lang.Shared
+import spock.lang.Specification
+
+class CalendarValidatorImplTest extends Specification {
+
+    @Shared
+    ContentBuilder builder
+
+    def setupSpec() {
+        builder = new ContentBuilder()
+    }
+
+    def 'test validation with custom rules'() {
+        given: 'a validator instance'
+        CalendarValidatorImpl validator = []
+
+        and: 'a calendar instance'
+        def calendar = builder.calendar() {
+            prodid '-//Ben Fortuna//iCal4j 1.0//EN'
+            version '2.0'
+            vevent {
+                uid '1'
+                dtstamp()
+                dtstart '20090810', parameters: parameters { value 'DATE' }
+                action 'DISPLAY'
+                attach new Attach(new File('gradle/wrapper/gradle-wrapper.jar').bytes)
+            }
+        }
+
+        when: 'validation applied to calendar instance'
+        validator.validate(calendar)
+
+        then: 'result is as expected'
+        notThrown(ValidationException)
+    }
+}