diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 6d233f55..0e0fa7a3 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -22,4 +22,4 @@ jobs:
         with:
           compiler: ${{ matrix.dc }}
       - name: Run tests
-        run: bin/test-all-exercises
+        run: bin/test-all-exercises -j 4
diff --git a/bin/test-all-exercises b/bin/test-all-exercises
index 8aec3e32..8576f195 100755
--- a/bin/test-all-exercises
+++ b/bin/test-all-exercises
@@ -1,22 +1,25 @@
 #!/bin/sh
 
-test_one=$(dirname $0)/test-exercise
-exercises=$(dirname $(dirname $0))/exercises
-status=0
-failed_exercises=""
-
-# TODO: To be confirmed: Would use this line when there are any concept exercises
-#for d in $exercises/{concept,practice}/*/; do
-for d in $exercises/practice/*; do
-  if ! $test_one $d; then
-    failed_exercises="$failed_exercises\n$(basename $d)"
-    status=1
-  fi
+jobs=1
+while getopts "j:" opt; do
+  case "$opt" in
+    j) jobs="$OPTARG" ;;
+    *) exit 1 ;;
+  esac
 done
 
-if [ $status -ne 0 ]; then
+test_one=$(dirname "$0")/test-exercise
+exercises=$(dirname "$(dirname "$0")")/exercises
+
+failed_file=$(mktemp)
+trap 'rm -f "$failed_file"' EXIT
+
+# shellcheck disable=SC2016
+cmd=$(printf '"%s" "$1" || basename "$1" >> "%s"' "$test_one" "$failed_file")
+printf '%s\n' "$exercises"/practice/*/ | xargs -P "$jobs" -I{} sh -c "${cmd}" _ "{}"
+
+if [ -s "$failed_file" ]; then
   echo "The following exercises failed"
-  echo $failed_exercises
+  cat "$failed_file"
+  exit 1
 fi
-
-exit $status
diff --git a/exercises/practice/roman-numerals/source/roman_numerals.d b/exercises/practice/roman-numerals/source/roman_numerals.d
index 812feb25..9fef77bb 100644
--- a/exercises/practice/roman-numerals/source/roman_numerals.d
+++ b/exercises/practice/roman-numerals/source/roman_numerals.d
@@ -14,7 +14,6 @@ unittest
 
     // one_yields_I
     {
-        writefln("Conversion of 1: %s", convert(1));
         assert("I" == convert(1));
     }
 
@@ -22,157 +21,131 @@ unittest
     {
         // two_yields_II
         {
-            writefln("Conversion of 2: %s", convert(2));
             assert("II" == convert(2));
         }
 
         // three_yields_III
         {
-            writefln("Conversion of 3: %s", convert(3));
             assert("III" == convert(3));
         }
 
         // four_yields_IV
         {
-            writefln("Conversion of 4: %s", convert(4));
             assert("IV" == convert(4));
         }
 
         // five_yields_V
         {
-            writefln("Conversion of 5: %s", convert(5));
             assert("V" == convert(5));
         }
 
         // six_yields_VI
         {
-            writefln("Conversion of 6: %s", convert(6));
             assert("VI" == convert(6));
         }
 
         // nine_yields_IX
         {
-            writefln("Conversion of 9: %s", convert(9));
             assert("IX" == convert(9));
         }
 
         // sixteen_yields_XVI
         {
-            writefln("Conversion of 16: %s", convert(16));
             assert("XVI" == convert(16));
         }
 
         // twenty_seven_yields_XXVII
         {
-            writefln("Conversion of 27: %s", convert(27));
             assert("XXVII" == convert(27));
         }
 
         // forty_eight_yields_XLVIII
         {
-            writefln("Conversion of 48: %s", convert(48));
             assert("XLVIII" == convert(48));
         }
 
         // forty_nine_yields_XLIX
         {
-            writefln("Conversion of 48: %s", convert(49));
             assert("XLIX" == convert(49));
         }
 
         // fifty_nine_yields_LIX
         {
-            writefln("Conversion of 59: %s", convert(59));
             assert("LIX" == convert(59));
         }
 
         // sixty_six_yields_LXVI
         {
-            writefln("Conversion of 66: %s", convert(66));
             assert("LXVI" == convert(66));
         }
 
         // ninety_three_yields_XCIII
         {
-            writefln("Conversion of 93: %s", convert(93));
             assert("XCIII" == convert(93));
         }
 
         // one_hundred_forty_one_yields_CXLI
         {
-            writefln("Conversion of 141: %s", convert(141));
             assert("CXLI" == convert(141));
         }
 
         // one_hundred_sixty_three_yields_CLXIII
         {
-            writefln("Conversion of 163: %s", convert(163));
             assert("CLXIII" == convert(163));
         }
 
         // one_hundred_sixty_six_yields_CLXVI
         {
-            writefln("Conversion of 166: %s", convert(166));
             assert("CLXVI" == convert(166));
         }
 
         // four_hundred_two_yields_CDII
         {
-            writefln("Conversion of 402: %s", convert(402));
             assert("CDII" == convert(402));
         }
 
         // five_hundred_seventy_five_yields_DLXXV
         {
-            writefln("Conversion of 575: %s", convert(575));
             assert("DLXXV" == convert(575));
         }
 
         // six_hundred_sixty_six_yields_DCLXVI
         {
-            writefln("Conversion of 666: %s", convert(666));
             assert("DCLXVI" == convert(666));
         }
 
         // nine_hundred_eleven_yields_CMXI
         {
-            writefln("Conversion of 911: %s", convert(911));
             assert("CMXI" == convert(911));
         }
 
         // one_thousand_twenty_four_yields_MXXIV
         {
-            writefln("Conversion of 1024: %s", convert(1024));
             assert("MXXIV" == convert(1024));
         }
 
         // one_thousand_six_hundred_sixty_six_yields_MDCLXVI
         {
-            writefln("Conversion of 1666: %s", convert(1666));
             assert("MDCLXVI" == convert(1666));
         }
 
         // three_thousand_yields_MMM
         {
-            writefln("Conversion of 3000: %s", convert(3000));
             assert("MMM" == convert(3000));
         }
 
         // three_thousand_one_yields_MMMI
         {
-            writefln("Conversion of 3001: %s", convert(3001));
             assert("MMMI" == convert(3001));
         }
 
         // three_thousand_eight_hundred_eighty_eight_yields_MMMDCCCLXXXVIII
         {
-            writefln("Conversion of 3888: %s", convert(3888));
             assert("MMMDCCCLXXXVIII" == convert(3888));
         }
 
         // three_thousand_nine_hundred_ninety_nine_yields_MMMCMXCIX
         {
-            writefln("Conversion of 3999: %s", convert(3999));
             assert("MMMCMXCIX" == convert(3999));
         }
     }