AWK write to a file based on number of fields in csv - bash

Question

I want to iterate over a csv file and discard the rows while writing to a file which doesnt have all columns in a row.
I have an input file mtest.csv like this
IP##Process##Device##ID
TestIP1##TestProcess2##TestDevice1##TestID1
TestIP2##TestProcess2##TestDevice2
TestIP3##TestProcess3##TestDevice3##TestID3
But I am trying to only write those row records where all the 4 columns are present. The output should not have the TestIP2 column complete row as it has 3 columns.
Sample output should look like this:
IP##Process##Device##ID
TestIP1##TestProcess2##TestDevice1##TestID1
TestIP3##TestProcess3##TestDevice3##TestID3
I used to do like this to get all the columns earlier but it writes the TestIP2 row as well which has 3 columns
awk -F "\##" '{print $1"\##"substr($2,1,50)"\##"substr($3,1,50)"\##"substr($4,1,50)}' mtest.csv >output2.csv
But when I try to ensure that it writes to file when all 4 columns are present, it doesn't work
awk -F "\##", 'NF >3 {print $1"\##"substr($2,1,50)"\##"substr($3,1,50)"\##"substr($4,1,50); exit}' mtest.csv >output2.csv

Answer 1

You are making things harder than it need to be. All you need to do is check NF==4 to output any records containing four fields. Your total awk expression would be:
awk -F'##' NF==4 < mtest.csv
(note: the default action by awk is print so there is no explicit print required.)
Example Use/Output
With your sample input in mtest.csv, you would receive:
$ awk -F'##' NF==4 < mtest.csv
IP##Process##Device##ID
TestIP1##TestProcess2##TestDevice1##TestID1
TestIP3##TestProcess3##TestDevice3##TestID3

Answer 2

Thanks David and vukung
Both your solutions are okay.I want to write to a file so that i can trim the length of each field as well
I think this below statement works out
awk -F "##" 'NF>3 {print $1"\##"substr($2,1,50)"\##"substr($3,1,2)"\##"substr($4,1,3)}' mtest.csv >output2.csv