Run tests in parallel, whenever possible

using tests/run-tests-parallel.sh script like:
MONERO_PARALLEL_TEST_JOBS=nproc tests/run-tests-parallel.sh

New target release-test-ci and MONERO_PARALLEL_TEST_JOBS var

.github/workflows/build.yml

@@ -124,4 +124,4 @@ jobs:
     - name: tests
       env:
         CTEST_OUTPUT_ON_FAILURE: ON
-      run: make release-test -j3
+      run: make release-test-ci -j3

Makefile

@@ -98,6 +98,10 @@ release-test:
 	mkdir -p $(builddir)/release
 	cd $(builddir)/release && cmake -D BUILD_TESTS=ON -D CMAKE_BUILD_TYPE=release $(topdir) && $(MAKE) && $(MAKE) test
 
+release-test-ci:
+	mkdir -p $(builddir)/release
+	cd $(builddir)/release && cmake -D BUILD_TESTS=ON -D CMAKE_BUILD_TYPE=release -D BUILD_SHARED_LIBS=ON $(topdir) && $(MAKE) && MONERO_PARALLEL_TEST_JOBS=nproc $(topdir)/tests/run-tests-parallel.sh
+
 release-all:
 	mkdir -p $(builddir)/release
 	cd $(builddir)/release && cmake -D BUILD_TESTS=ON -D CMAKE_BUILD_TYPE=release $(topdir) && $(MAKE)

tests/run-tests-parallel.sh

@@ -0,0 +1,68 @@
+#!/bin/bash -e
+
+# Copyright (c) 2014-2021, The Monero Project
+#
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification, are
+# permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice, this list of
+#    conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice, this list
+#    of conditions and the following disclaimer in the documentation and/or other
+#    materials provided with the distribution.
+#
+# 3. Neither the name of the copyright holder nor the names of its contributors may be
+#    used to endorse or promote products derived from this software without specific
+#    prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+# THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+# STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+# THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# The parallelism celing can be controlled with MONERO_PARALLEL_TEST_JOBS env variable,
+# for example:
+#
+# MONERO_PARALLEL_TEST_JOBS=1     tests/run-tests-parallel.sh
+# MONERO_PARALLEL_TEST_JOBS=nproc tests/run-tests-parallel.sh
+#
+# The minimum between the ceiling and a currently selected reasonable number of threads is used in the end.
+# The reasonable number is selected as a number, that delivers the solution in the shortest time.
+
+NUM_PROC_MAX_REASONABLE=2 # This might be increased, once the core_tests are divided into many more independent pieces or simply sped up
+TESTS_EXCLUDED_REGEX="unit_tests|functional_tests_rpc" # These tests collide with core_tests
+
+if [ -z $MONERO_PARALLEL_TEST_JOBS ]; then
+	echo "No parallelism ceiling selected. Using nproc."
+	MONERO_PARALLEL_TEST_JOBS=$(nproc)
+else
+	if [ "$MONERO_PARALLEL_TEST_JOBS" == "nproc" ]; then
+		MONERO_PARALLEL_TEST_JOBS=$(nproc)
+	fi
+	echo "Parallelism ceiling selected. Using $MONERO_PARALLEL_TEST_JOBS jobs."
+fi
+
+
+min() {
+	RET=$(($1 < $2 ? $1 : $2))
+	echo $RET
+}
+
+NUM_PROC_FINAL=$(min $NUM_PROC_MAX_REASONABLE $MONERO_PARALLEL_TEST_JOBS)
+echo "Job number ceiling is $MONERO_PARALLEL_TEST_JOBS and the reasonable maximum is currently $NUM_PROC_MAX_REASONABLE."
+echo "Using the minimum of the two, so $NUM_PROC_FINAL jobs."
+
+# Run the excluded tests first, then everything but excluded.
+# In the current situation, the excluded tests are the most probable and quickest to fail, giving an early feedback.
+time \
+ctest -j"${NUM_PROC_FINAL}" -R "${TESTS_EXCLUDED_REGEX}" && \
+ctest -j"${NUM_PROC_FINAL}" -E "${TESTS_EXCLUDED_REGEX}"
+