issue-128 : Add regression test for headers writing with no data

Signed-off-by: Peter Ansell <[email protected]>

src/test/java/com/fasterxml/jackson/dataformat/csv/ser/HeaderWriteTest.java

@@ -0,0 +1,61 @@
+package com.fasterxml.jackson.dataformat.csv.ser;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.Arrays;
+import java.util.List;
+
+import com.fasterxml.jackson.databind.SequenceWriter;
+import com.fasterxml.jackson.dataformat.csv.*;
+
+// Tests for verifying that headers are emitted
+public class HeaderWriteTest extends ModuleTestBase
+{
+    /*
+    /**********************************************************************
+    /* Test methods
+    /**********************************************************************
+     */
+
+    private final CsvMapper MAPPER = mapperForCsv();
+
+    public void testNoLines() throws Exception
+    {
+        List<String> headers = Arrays.asList("TestHeader1", "TestHeader2");
+    	List<List<String>> dataSource = Arrays.asList();
+		String result = runTest(headers, dataSource);
+
+		assertEquals("Headers should have been written even with no other data", "TestHeader1,TestHeader2\n", result);
+    }
+
+    public void testOneLine() throws Exception
+    {
+        List<String> headers = Arrays.asList("TestHeader1", "TestHeader2");
+    	List<List<String>> dataSource = Arrays.asList(Arrays.asList("TestValue1", "TestValue2"));
+		String result = runTest(headers, dataSource);
+
+		assertEquals("Headers should have been written before line", "TestHeader1,TestHeader2\nTestValue1,TestValue2\n", result);
+    }
+
+    private String runTest(List<String> headers, List<List<String>> dataSource) throws IOException 
+    {
+        StringWriter writer = new StringWriter();
+
+        CsvSchema.Builder builder = CsvSchema.builder();
+        for (String nextHeader : headers) {
+            builder = builder.addColumn(nextHeader);
+        }
+
+        CsvSchema schema = builder.setUseHeader(true).build();
+        try (SequenceWriter csvWriter = MAPPER.writerWithDefaultPrettyPrinter()
+        		                              .with(schema)
+        		                              .forType(List.class)
+        		                              .writeValues(writer);) {
+            for(List<String> nextRow : dataSource) {
+            	csvWriter.write(nextRow);
+            }
+        }
+
+		return writer.toString();
+    }
+}