diff --git a/runner/main/jobtypes/phpunit/phpunit.sh b/runner/main/jobtypes/phpunit/phpunit.sh
index ac24bc8..8249506 100644
--- a/runner/main/jobtypes/phpunit/phpunit.sh
+++ b/runner/main/jobtypes/phpunit/phpunit.sh
@@ -62,6 +62,10 @@ function phpunit_to_summary() {
     echo "== PHPUNIT_FILTER: ${PHPUNIT_FILTER}"
     echo "== PHPUNIT_TESTSUITE: ${PHPUNIT_TESTSUITE}"
     echo "== MOODLE_CONFIG: ${MOODLE_CONFIG}"
+    if [[ -n "${GOOD_COMMIT}" ]] || [[ -n "${BAD_COMMIT}" ]]; then
+        echo "== GOOD_COMMIT: ${GOOD_COMMIT}"
+        echo "== BAD_COMMIT: ${BAD_COMMIT}"
+    fi
 }
 
 # This job type defines the following env variables
@@ -106,7 +110,7 @@ function phpunit_check() {
     verify_modules $(phpunit_modules)
 
     # These env variables must be set for the job to work.
-    verify_env UUID ENVIROPATH WEBSERVER
+    verify_env UUID ENVIROPATH WEBSERVER GOOD_COMMIT BAD_COMMIT
 }
 
 # PHPUnit job type init.
@@ -116,23 +120,62 @@ function phpunit_config() {
     PHPUNIT_FILTER="${PHPUNIT_FILTER:-}"
     PHPUNIT_TESTSUITE="${PHPUNIT_TESTSUITE:-}"
     EXITCODE=0
+
+    # If GOOD_COMMIT and BAD_COMMIT are set, it means that we are going to run a bisect
+    # session, so we need to enable FULLGIT (to get access to complete repository clone).
+    if [[ -n "${GOOD_COMMIT}" ]] && [[ -n "${BAD_COMMIT}" ]]; then
+        FULLGIT="yes"
+        # Also, we don't want to allow repetitions in the bisect session.
+        RUNCOUNT=1
+    fi
 }
 
 # PHPUnit job type setup.
 function phpunit_setup() {
+    # If one of GOOD_COMMIT or BAD_COMMIT are not set, but the other is, error out.
+    if [[ -n "${GOOD_COMMIT}" ]] && [[ -z "${BAD_COMMIT}" ]]; then
+        exit_error "GOOD_COMMIT is set but BAD_COMMIT is not set."
+    fi
+    if [[ -z "${GOOD_COMMIT}" ]] && [[ -n "${BAD_COMMIT}" ]]; then
+        exit_error "BAD_COMMIT is set but GOOD_COMMIT is not set."
+    fi
+    # If both GOOD_COMMIT and BAD_COMMIT are set and they are the same, error out.
+    if [[ -n "${GOOD_COMMIT}" ]] && [[ -n "${BAD_COMMIT}" ]] && [[ "${GOOD_COMMIT}" == "${BAD_COMMIT}" ]]; then
+        exit_error "GOOD_COMMIT and BAD_COMMIT are set, but they are the same."
+    fi
+
+    # If both GOOD_COMMIT and BAD_COMMIT are not set, we are going to run a normal session.
+    # (for bisect sessions we don't have to setup the environment).
+    if [[ -z "${GOOD_COMMIT}" ]] && [[ -z "${BAD_COMMIT}" ]]; then
+        phpunit_setup_normal
+    fi
+}
+
+# PHPUnit job type setup for normal mode.
+function phpunit_setup_normal() {
     # Init the PHPUnit site.
     echo
     echo ">>> startsection Initialising PHPUnit environment at $(date)<<<"
     echo "============================================================================"
     docker exec -t -u www-data "${WEBSERVER}" \
-        php admin/tool/phpunit/cli/init.php \
-            --force
+        php admin/tool/phpunit/cli/init.php
     echo "============================================================================"
     echo ">>> stopsection <<<"
 }
 
 # PHPUnit job type run.
 function phpunit_run() {
+    # If both GOOD_COMMIT and BAD_COMMIT are not set, we are going to run a normal session.
+    if [[ -z "${GOOD_COMMIT}" ]] && [[ -z "${BAD_COMMIT}" ]]; then
+        phpunit_run_normal
+    else
+        # If GOOD_COMMIT and BAD_COMMIT are set, we are going to run a bisect session.
+        phpunit_run_bisect
+    fi
+}
+
+# PHPUnit job tye run for normal mode.
+function phpunit_run_normal() {
     # Run the job type.
     echo
     if [[ RUNCOUNT -gt 1 ]]; then
@@ -163,11 +206,66 @@ function phpunit_run() {
     while [[ ${iter} -le ${RUNCOUNT} ]]; do
         echo
         echo ">>> PHPUnit run ${iter} at $(date) <<<"
-        docker exec -t "${WEBSERVER}" "${cmd[@]}"
+        docker exec -t -u www-data "${WEBSERVER}" "${cmd[@]}"
         EXITCODE=$((EXITCODE + $?))
         iter=$((iter+1))
     done
 
     echo "============================================================================"
     echo ">>> stopsection <<<"
-}
\ No newline at end of file
+}
+
+# PHPUnit job tye run for bisect mode.
+function phpunit_run_bisect() {
+    # Run the job type.
+    echo
+    echo ">>> startsection Starting PHPUnit bisect session at $(date) <<<"
+    echo "=== Good commit: ${GOOD_COMMIT}"
+    echo "=== Bad commit: ${BAD_COMMIT}"
+    echo "============================================================================"
+    # Start the bisect session.
+    docker exec -t -u www-data "${WEBSERVER}" \
+        git bisect start "${BAD_COMMIT}" "${GOOD_COMMIT}"
+
+    # Build the int command.
+    local initcmd=(
+        php admin/tool/phpunit/cli/init.php
+    )
+    # Build the run command.
+    local runcmd=(
+        php vendor/bin/phpunit
+        --disallow-test-output
+        --fail-on-risky
+        --verbose
+    )
+    if [[ -n "${PHPUNIT_FILTER}" ]]; then
+        runcmd+=(--filter "${PHPUNIT_FILTER}")
+    fi
+    if [[ -n "${PHPUNIT_TESTSUITE}" ]]; then
+        runcmd+=(--testsuite "${PHPUNIT_TESTSUITE}")
+    fi
+
+    # Generate the bisect.sh script that we are going to use to run the phpunit bisect session.
+    # (it runs both init and run commands together).
+    docker exec -i -u www-data "${WEBSERVER}" \
+        bash -c "cat > bisect.sh" <<- EOF
+			#!/bin/bash
+			${initcmd[*]} >/dev/null 2>&1; ${runcmd[*]}
+			exitcode=\$?
+			echo "============================================================================"
+			exit \$exitcode
+			EOF
+
+    # Run the bisect session.
+    echo "============================================================================"
+    docker exec -u www-data "${WEBSERVER}" \
+        git bisect run bash bisect.sh
+    EXITCODE=$?
+
+    # Finish the bisect session.
+    docker exec -u www-data "${WEBSERVER}" \
+        git bisect reset
+
+    echo "============================================================================"
+    echo ">>> stopsection <<<"
+}
diff --git a/runner/main/modules/docker-php/docker-php.sh b/runner/main/modules/docker-php/docker-php.sh
index 75e3d52..d438b79 100644
--- a/runner/main/modules/docker-php/docker-php.sh
+++ b/runner/main/modules/docker-php/docker-php.sh
@@ -58,6 +58,9 @@ function docker-php_setup() {
       -v "${SHAREDDIR}":/shared \
       "${DOCKER_PHP}"
 
+    # Ensure that the whole .composer directory is writable to all (www-data needs to write there).
+    docker exec "${WEBSERVER}" chmod -R go+rw /var/www/.composer
+
     echo
     echo "Webserver logs:"
     docker logs "${WEBSERVER}"
diff --git a/runner/main/modules/git/git.sh b/runner/main/modules/git/git.sh
index a2495eb..7ffeadf 100644
--- a/runner/main/modules/git/git.sh
+++ b/runner/main/modules/git/git.sh
@@ -21,6 +21,8 @@
 function git_env() {
     env=(
         GIT_COMMIT
+        GOOD_COMMIT
+        BAD_COMMIT
     )
     echo "${env[@]}"
 }
diff --git a/runner/main/modules/moodle-core-copy/moodle-core-copy.sh b/runner/main/modules/moodle-core-copy/moodle-core-copy.sh
index 1b774e3..c709637 100644
--- a/runner/main/modules/moodle-core-copy/moodle-core-copy.sh
+++ b/runner/main/modules/moodle-core-copy/moodle-core-copy.sh
@@ -74,7 +74,7 @@ function moodle-core-copy_setup() {
         fi
 
         # If the repository was cloned shallow (--depth), un-shallow it.
-        if (docker exec -u www-data "${WEBSERVER}" git rev-parse --is-shallow-repository); then
+        if (docker exec -u www-data "${WEBSERVER}" git rev-parse --is-shallow-repository | grep -q 'true'); then
             echo "== Unshallowing the repository."
             docker exec -u www-data "${WEBSERVER}" git fetch --unshallow
         fi
@@ -91,17 +91,20 @@ function moodle-core-copy_setup() {
     # Copy the config.php in place
     echo "== Copying configuration in place."
     docker cp "${BASEDIR}/modules/docker-php/config.template.php" "${WEBSERVER}":/var/www/html/config.php
+    docker exec "${WEBSERVER}" chown -R www-data:www-data /var/www/html/config.php
 
     # Copy the plugins in place.
     if [[ -n "$PLUGINSTOINSTALL" ]]; then
-      echo "== Copying external plugins in place."
-      docker cp "${PLUGINSDIR}"/. "${WEBSERVER}":/var/www/html
+        echo "== Copying external plugins in place."
+        docker cp "${PLUGINSDIR}"/. "${WEBSERVER}":/var/www/html
+        docker exec "${WEBSERVER}" chown -R www-data:www-data /var/www/html
     fi
 
     # Copy composer-phar if available in caches.
     if [[ -f "${COMPOSERCACHE}/composer.phar" ]]; then
-      echo "== Copying composer.phar in place."
-      docker cp "${COMPOSERCACHE}/composer.phar" "${WEBSERVER}":/var/www/html/composer.phar
+        echo "== Copying composer.phar in place."
+        docker cp "${COMPOSERCACHE}/composer.phar" "${WEBSERVER}":/var/www/html/composer.phar
+        docker exec "${WEBSERVER}" chown -R www-data:www-data /var/www/html/composer.phar
     fi
 
     echo "============================================================================"