Is it possible to run map/reduce job on Hadoop cluster with no input file?

File paths are relevant for FileInputFormat based inputs like SequenceInputFormat, etc. But inputformats that read from hbase, database do not read from files, so you could make your own implementation of the InputFormat and define your own behaviour in getSplits, RecordReader, createRecordReader. For insperation look into the source code of the TextInputFormat class.

For MR job unit testing you can also use MRUnit .If you want to generate test data with Hadoop, then I'd recommend you to have a look at the source code of Teragen .

I guess your are looking to test your map-reduce on samll set of data so in that case i will recommand following

Unit Test For Map-Reduce will solve your problem

If you want to test your mapper/combiner/reducer for a single line of linput from your file , best possible thing is to use UnitTest for each .

sample code:-
using Mocking Frame work in java Use can run these test cases in your IDE

Here i have used Mockito OR MRunit can also be used which too is depended on a Mockito(Java Mocking Framework)

public class BoxPlotMapperTest {@Testpublic void validOutputTextMapper() throws IOException, InterruptedException{    Mapper mapper=new Mapper();//Your Mapper Object     Text line=new Text("single line from input-file"); // single line input from file     Mapper.Context context=Mockito.mock(Mapper.Context.class);    mapper.map(null, line, context);//(key=null,value=line,context)//key was not used in my code so its null     Mockito.verify(context).write(new Text("your expected key-output"), new Text("your expected value-output")); // }@Testpublic void validOutputTextReducer() throws IOException, InterruptedException{    Reducer reduer=new Reducer();    final List<Text> values=new ArrayList<Text>();    values.add(new Text("value1"));    values.add(new Text("value2"));    values.add(new Text("value3"));    values.add(new Text("value4"));    Iterable<Text> iterable=new Iterable<Text>() {        @Override        public Iterator<Text> iterator() {            // TODO Auto-generated method stub            return values.iterator();        }    };    Reducer.Context context=Mockito.mock(Reducer.Context.class);    reduer.reduce(new Text("key"),iterable, context);    Mockito.verify(context).write(new Text("your expected key-output"), new Text("your expected value-output"));}

}