diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index 5064aa62..4237086c 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -15,9 +15,9 @@ jobs:
     - uses: actions/checkout@v3
     - run: sudo apt install -y llvm-${{ matrix.llvm-version }}-dev clang-${{ matrix.llvm-version }} make valgrind
     - run: LLVM_CONFIG=llvm-config-${{ matrix.llvm-version }} make
-    - run: ./runtests.sh './jou ${{ matrix.opt-level }} %s'
-    - run: ./runtests.sh './jou ${{ matrix.opt-level }} --verbose %s'
-    - run: ./runtests.sh --valgrind './jou ${{ matrix.opt-level }} %s'
+    - run: ./runtests.sh --verbose './jou ${{ matrix.opt-level }} %s'
+    - run: ./runtests.sh --verbose './jou ${{ matrix.opt-level }} --verbose %s'
+    - run: ./runtests.sh --verbose --valgrind './jou ${{ matrix.opt-level }} %s'
     # valgrind+verbose isn't meaningful: test script would ignore valgrind output
 
   fuzzer:
diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index 67b086b7..53d4893a 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -126,7 +126,7 @@ jobs:
         shell: bash
       - run: cd "test dir" && ./jou.exe --verbose examples/hello.jou
         shell: bash
-      - run: cd "test dir" && ./runtests.sh
+      - run: cd "test dir" && ./runtests.sh --verbose
         shell: bash
 
   fuzzer:
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index f45f5e0c..bf8c5003 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -101,7 +101,7 @@ $ ./runtests.sh
 
 This command does a few things:
 - If not on Windows, it compiles the Jou compiler if you have changed something in `src/` since the last time it was compiled. (On Windows you need to use the build button in CodeBlocks to compile.)
-- It runs all Jou files in `examples/` and `tests/`
+- It runs all Jou files in `examples/` and `tests/`. To speed things up, it runs two files in parallel.
 - It ensures that the Jou files output what is expected.
 
 The expected output is auto-generated from comments in the Jou files:
diff --git a/runtests.sh b/runtests.sh
index b32539c9..da0c7800 100755
--- a/runtests.sh
+++ b/runtests.sh
@@ -11,12 +11,22 @@
 export LANG=C  # "Segmentation fault" must be in english for this script to work
 set -e -o pipefail
 
-if [ "$1" == "--valgrind" ]; then
-    valgrind=yes
-    shift
-else
-    valgrind=no
-fi
+function usage() {
+    echo "Usage: $0 [--valgrind] [--verbose] [TEMPLATE]" >&2
+    echo "TEMPLATE can be e.g. './jou %s', where %s will be replaced by a jou file." >&2
+    exit 2
+}
+
+valgrind=no
+verbose=no
+
+while [[ "$1" =~ ^- ]]; do
+    case "$1" in
+        --valgrind) valgrind=yes; shift ;;
+        --verbose) verbose=yes; shift ;;
+        *) usage ;;
+    esac
+done
 
 if [ $# == 0 ]; then
     # No arguments --> run tests in the basic/simple way
@@ -25,12 +35,10 @@ if [ $# == 0 ]; then
     else
         command_template='./jou %s'
     fi
-elif [ $# == 1 ] && [[ "$1" =~ ^[^-] ]]; then
+elif [ $# == 1 ]; then
     command_template="$1"
 else
-    echo "Usage: $0 [--valgrind] [TEMPLATE]" >&2
-    echo "TEMPLATE can be e.g. './jou %s', where %s will be replaced by a jou file." >&2
-    exit 2
+    usage
 fi
 
 if [ $valgrind = yes ]; then
@@ -106,6 +114,18 @@ GREEN="\x1b[32m"
 RED="\x1b[31m"
 RESET="\x1b[0m"
 
+if [ $verbose = yes ]; then
+    function show_run() { echo "run: $1"; }
+    function show_skip() { echo -e "${YELLOW}skip${RESET} $1"; }
+    function show_ok() { echo -e "${GREEN}ok${RESET}   $1"; }
+    function show_fail() { echo -e "${RED}FAIL${RESET} $1"; }
+else
+    function show_run() { true; }
+    function show_skip() { echo -ne ${YELLOW}s${RESET}; }
+    function show_ok() { echo -ne ${GREEN}.${RESET}; }
+    function show_fail() { echo -ne ${RED}F${RESET}; }
+fi
+
 function run_test()
 {
     local joufile="$1"
@@ -122,20 +142,22 @@ function run_test()
     if ( [[ "$command_template" =~ -O[1-3] ]] && [[ $joufile =~ ^tests/crash/ ]] ) \
         || ( [[ "$command_template" =~ valgrind ]] && [ $correct_exit_code != 0 ] )
     then
-        # Skip
-        echo -ne ${YELLOW}s${RESET}
+        show_skip $joufile
         mv $diffpath $diffpath.skip
-    elif diff -u --color=always \
+        return
+    fi
+
+    show_run $joufile
+    if diff -u --color=always \
         <(generate_expected_output $joufile $correct_exit_code | tr -d '\r') \
         <(ulimit -v 500000 2>/dev/null; bash -c "$command; echo Exit code: \$?" 2>&1 | post_process_output $joufile | tr -d '\r') \
         &>> $diffpath
     then
-        # Ran successfully
-        echo -ne ${GREEN}.${RESET}
+        show_ok $joufile
         rm -f $diffpath
     else
-        # Failed
-        echo -ne ${RED}F${RESET}
+        show_fail $joufile
+        # Do not delete diff file. It will be displayed at end of test run.
     fi
 }