Fix and add unit tests for issue 3071 - adaptive sampler runs on models w/ zero params. #1329

	name: Testing

	env:
	clangppVersion: '6.0'

	on:
	pull_request:
	branches: [ develop, master ]
	push:
	branches: [ develop, master ]
	paths-ignore:
	- 'licenses/**'
	- 'LICENSE.md'
	- 'README.md'
	- 'RELEASE-NOTES.txt'
	workflow_dispatch:

	jobs:
	run-tests:
	name: run stan tests
	runs-on: ${{ matrix.os }}
	strategy:
	matrix:
	os: [ubuntu-20.04]
	python-version: [3.8]
	fail-fast: false
	steps:
	- name: Check out source code
	uses: actions/checkout@v3
	with:
	submodules: true
	- name: Install clang++
	run: sudo apt-get install clang-${{ env.clangppVersion }}++
	- name: Run tests
	run: \|
	echo "CXX=clang++-${{ env.clangppVersion }}" >> make/local
	echo "O=0" >> make/local
	python runTests.py -j 2 src/test/unit

	run-fvar-var-tests:
	name: run stan fvar-var model tests
	runs-on: ${{ matrix.os }}
	strategy:
	matrix:
	os: [ubuntu-20.04]
	python-version: [3.8]
	fail-fast: false
	steps:
	- name: Check out source code
	uses: actions/checkout@v3
	with:
	submodules: true
	- name: Install clang++
	run: sudo apt-get install clang-${{ env.clangppVersion }}++
	- name: Run tests
	run: \|
	echo "CXX=clang++-${{ env.clangppVersion }}" >> make/local
	echo "CXXFLAGS+=-DSTAN_MODEL_FVAR_VAR" >> make/local
	echo "O=0" >> make/local
	python runTests.py -j 2 src/test/unit/model/

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