Is there anyway to merge cobertura coverage xml reports together?

The simplest utility I've found for merging Cobertura files is cobertura-merge via NPM.

Usage:

npm install cobertura-merge
cobertura -merge -o output.xml package1=input1.xml package2=input2.xml

Or it can be used directly without installing through npx:

npx cobertura-merge -o output.xml package1=input1.xml package2=input2.xml

Examples sourced from the GitHub README for cobertura-merge.

It seems you're using gcovr. Since version 4.2, gcovr can merge its JSON reports with the -a option. So you could do:

# run test1
./test1
gcovr ... --xml coverage-test1.xml --json coverage-test1.json
find . -type f -name '*.gcda' -exec rm {} +

# run test2
./test2
gcovr ... --xml coverage-test2.xml --json coverage-test2.json
find . -type f -name '*.gcda' -exec rm {} +

# combine JSON reports
gcovr -a coverage-test1.json -a coverage-test2.json --xml coverage-combined.xml

The last release of ReportGenerator can merge cobertura files.

You can install it from nuget

usage:

reportgenerator "-reports:target\*\*.xml" "-targetdir:C:\report" -reporttypes:Cobertura

A file Corbertura.xml is generated in the targetdir directory

You can use the dotnet core version to use it on linux or mac