[CSV-257] Updating from 1.6 to 1.7 breaks a header line with a missing

header name

Document the current behavior: Throw a IllegalArgumentException is a
header name is missing.

Author: garydgregory

src/test/java/org/apache/commons/csv/issues/JiraCsv257Test.java

@@ -0,0 +1,84 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.commons.csv.issues;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.IOException;
+import java.io.StringReader;
+
+import org.apache.commons.csv.CSVFormat;
+import org.apache.commons.csv.CSVParser;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests https://issues.apache.org/jira/browse/CSV-257
+ */
+class JiraCsv257Test {
+
+    private static final String INPUT = ",";
+
+    @Test
+    void testHeaderBuilder() throws IOException {
+        // @formatter:off
+        final CSVFormat format = CSVFormat.RFC4180.builder()
+                .setDelimiter(INPUT.charAt(0))
+                .setHeader()
+                .setSkipHeaderRecord(true)
+                .setIgnoreSurroundingSpaces(true)
+                .get();
+        // @formatter:on
+        // Document the current behavior: Throw a IllegalArgumentException is a header name is missing.
+        assertThrows(IllegalArgumentException.class, () -> {
+            try (CSVParser parser = CSVParser.parse(INPUT, format)) {
+                // empty
+            }
+        });
+    }
+
+    @Test
+    void testHeaderDepreacted() throws IOException {
+        // @formatter:off
+        final CSVFormat format = CSVFormat.RFC4180
+                .withDelimiter(INPUT.charAt(0))
+                .withFirstRecordAsHeader()
+                .withIgnoreSurroundingSpaces();
+        // @formatter:on
+        // Document the current behavior: Throw a IllegalArgumentException is a header name is missing.
+        assertThrows(IllegalArgumentException.class, () -> {
+            try (CSVParser parser = new CSVParser(new StringReader(INPUT), format)) {
+                // empty
+            }
+        });
+    }
+
+    @Test
+    void testNoHeaderBuilder() throws IOException {
+        // @formatter:off
+        final CSVFormat format = CSVFormat.RFC4180.builder()
+                .setDelimiter(INPUT.charAt(0))
+                .setIgnoreSurroundingSpaces(true)
+                .get();
+        // @formatter:on
+        try (CSVParser parser = CSVParser.parse(INPUT, format)) {
+            // empty
+        }
+    }
+}