Hello All,

for estimating the differential expression values,what statistical test does DEseq2 use for estimating the differential expression values,is it t-test, Fisher exact test or some other?

For the methodological details of DESeq2, you should check Chapter 4 of the manual, "Theory Behind DESeq2". There, you'll find that the default test is the Wald test, with the likelihood ratio test as an alternative option.