diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3ffce21..d416f74 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -49,6 +49,23 @@ jobs:
       - run: rustup component add clippy
       - run: cargo clippy -- -D warnings
 
+  gnu-testsuite:
+    name: GNU test suite
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo build --release
+      # do not fail, the report is merely informative (at least until all tests pass reliably)
+      - run: ./tests/run-upstream-testsuite.sh release || true
+        env:
+          TERM: xterm
+      - uses: actions/upload-artifact@v4
+        with:
+          name: test-results.json
+          path: tests/test-results.json
+      - run: ./tests/print-test-results.sh tests/test-results.json
+
   coverage:
     name: Code Coverage
     runs-on: ${{ matrix.job.os }}
diff --git a/tests/print-test-results.sh b/tests/print-test-results.sh
new file mode 100755
index 0000000..23136d6
--- /dev/null
+++ b/tests/print-test-results.sh
@@ -0,0 +1,38 @@
+#!/bin/bash
+
+# Print the test results written to a JSON file by run-upstream-testsuite.sh
+# in a markdown format. The printout includes the name of the test, the result,
+# the URL to the test script and the contents of stdout and stderr.
+# It can be used verbatim as the description when filing an issue for a test
+# with an unexpected result.
+
+json="test-results.json"
+[[ -n $1 ]] && json="$1"
+
+codeblock () { echo -e "\`\`\`\n$1\n\`\`\`"; }
+
+jq -c '.tests[]' "$json" | while read -r test
+do
+  name=$(echo "$test" | jq -r '.test')
+  echo "# test: $name"
+  result=$(echo "$test" | jq -r '.result')
+  echo "result: $result"
+  url=$(echo "$test" | jq -r '.url')
+  echo "url: $url"
+  if [[ "$result" != "SKIP" ]]
+  then
+    stdout=$(echo "$test" | jq -r '.stdout' | base64 -d)
+    if [[ -n "$stdout" ]]
+    then
+      echo "## stdout"
+      codeblock "$stdout"
+    fi
+    stderr=$(echo "$test" | jq -r '.stderr' | base64 -d)
+    if [[ -n "$stderr" ]]
+    then
+      echo "## stderr"
+      codeblock "$stderr"
+    fi
+  fi
+  echo ""
+done
diff --git a/tests/run-upstream-testsuite.sh b/tests/run-upstream-testsuite.sh
new file mode 100755
index 0000000..d85dfd6
--- /dev/null
+++ b/tests/run-upstream-testsuite.sh
@@ -0,0 +1,141 @@
+#!/bin/bash
+
+# Run the GNU upstream test suite for diffutils against a local build of the
+# Rust implementation, print out a summary of the test results, and writes a
+# JSON file ('test-results.json') containing detailed information about the
+# test run.
+
+# The JSON file contains metadata about the test run, and for each test the
+# result as well as the contents of stdout, stderr, and of all the files
+# written by the test script, if any (excluding subdirectories).
+
+# The script takes a shortcut to fetch only the test suite from the upstream
+# repository and carefully avoids running the autotools machinery which is
+# time-consuming and resource-intensive, and doesn't offer the option to not
+# build the upstream binaries. As a consequence, the environment in which the
+# tests are run might not match exactly that used when the upstream tests are
+# run through the autotools.
+
+# By default it expects a release build of the diffutils binary, but a
+# different build profile can be specified as an argument
+# (e.g. 'dev' or 'test').
+# Unless overriden by the $TESTS environment variable, all tests in the test
+# suite will be run. Tests targeting a command that is not yet implemented
+# (e.g. cmp, diff3 or sdiff) are skipped.
+
+scriptpath=$(dirname "$(readlink -f "$0")")
+rev=$(git rev-parse HEAD)
+
+# Allow passing a specific profile as parameter (default to "release")
+profile="release"
+[[ -n $1 ]] && profile="$1"
+
+# Verify that the diffutils binary was built for the requested profile
+binary="$scriptpath/../target/$profile/diffutils"
+if [[ ! -x "$binary" ]]
+then
+  echo "Missing build for profile $profile"
+  exit 1
+fi
+
+# Work in a temporary directory
+tempdir=$(mktemp -d)
+cd "$tempdir"
+
+# Check out the upstream test suite
+gitserver="https://git.savannah.gnu.org"
+testsuite="$gitserver/git/diffutils.git"
+echo "Fetching upstream test suite from $testsuite"
+git clone -n --depth=1 --filter=tree:0 "$testsuite" &> /dev/null
+cd diffutils
+git sparse-checkout set --no-cone tests &> /dev/null
+git checkout &> /dev/null
+upstreamrev=$(git rev-parse HEAD)
+
+# Ensure that calling `diff` invokes the built `diffutils` binary instead of
+# the upstream `diff` binary that is most likely installed on the system
+mkdir src
+cd src
+ln -s "$binary" diff
+cd ../tests
+
+if [[ -n "$TESTS" ]]
+then
+  tests="$TESTS"
+else
+  # Get a list of all upstream tests (default if $TESTS isn't set)
+  echo -e '\n\nprinttests:\n\t@echo "${TESTS}"' >> Makefile.am
+  tests=$(make -f Makefile.am printtests)
+fi
+total=$(echo "$tests" | wc -w)
+echo "Running $total tests"
+export LC_ALL=C
+export KEEP=yes
+exitcode=0
+timestamp=$(date -Iseconds)
+urlroot="$gitserver/cgit/diffutils.git/tree/tests/"
+passed=0
+failed=0
+skipped=0
+normal="$(tput sgr0)"
+for test in $tests
+do
+  result="FAIL"
+  url="$urlroot$test?id=$upstreamrev"
+  # Run only the tests that invoke `diff`,
+  # because other binaries aren't implemented yet
+  if ! grep -E -s -q "(cmp|diff3|sdiff)" "$test"
+  then
+    sh "$test" 1> stdout.txt 2> stderr.txt && result="PASS" || exitcode=1
+    json+="{\"test\":\"$test\",\"result\":\"$result\","
+    json+="\"url\":\"$url\","
+    json+="\"stdout\":\"$(base64 -w0 < stdout.txt)\","
+    json+="\"stderr\":\"$(base64 -w0 < stderr.txt)\","
+    json+="\"files\":{"
+    cd gt-$test.*
+    # Note: this doesn't include the contents of subdirectories,
+    # but there isn't much value added in doing so
+    for file in *
+    do
+      [[ -f "$file" ]] && json+="\"$file\":\"$(base64 -w0 < "$file")\","
+    done
+    json="${json%,}}},"
+    cd - > /dev/null
+    [[ "$result" = "PASS" ]] && (( passed++ ))
+    [[ "$result" = "FAIL" ]] && (( failed++ ))
+  else
+    result="SKIP"
+    (( skipped++ ))
+    json+="{\"test\":\"$test\",\"url\":\"$url\",\"result\":\"$result\"},"
+  fi
+  color=2 # green
+  [[ "$result" = "FAIL" ]] && color=1 # red
+  [[ "$result" = "SKIP" ]] && color=3 # yellow
+  printf "  %-40s $(tput setaf $color)$result$(tput sgr0)\n" "$test"
+done
+echo ""
+echo -n "Summary: TOTAL: $total / "
+echo -n "$(tput setaf 2)PASS$normal: $passed / "
+echo -n "$(tput setaf 1)FAIL$normal: $failed / "
+echo "$(tput setaf 3)SKIP$normal: $skipped"
+echo ""
+
+json="\"tests\":[${json%,}]"
+metadata="\"timestamp\":\"$timestamp\","
+metadata+="\"revision\":\"$rev\","
+metadata+="\"upstream-revision\":\"$upstreamrev\","
+if [[ -n "$GITHUB_ACTIONS" ]]
+then
+  metadata+="\"branch\":\"$GITHUB_REF\","
+fi
+json="{$metadata $json}"
+
+# Clean up
+cd "$scriptpath"
+rm -rf "$tempdir"
+
+resultsfile="test-results.json"
+echo "$json" | jq > "$resultsfile"
+echo "Results written to $scriptpath/$resultsfile"
+
+exit $exitcode