Ladybird+Tests/LibWeb: Add very basic text-only test harness

This allows us to create "text tests" in addition to "layout tests".
Text tests work the same as layout tests, but dump the document content
as text and exit upon receiving the window "load" event.

Ladybird/CMakeLists.txt

@@ -170,4 +170,10 @@ if (BUILD_TESTING)
         COMMAND ${SERENITY_SOURCE_DIR}/Tests/LibWeb/Layout/layout_test.sh ${CMAKE_CURRENT_BINARY_DIR}
     )
     set_tests_properties(Layout PROPERTIES ENVIRONMENT QT_QPA_PLATFORM=offscreen)
+
+    add_test(
+        NAME LibWebText
+        COMMAND ${SERENITY_SOURCE_DIR}/Tests/LibWeb/Text/text_test.sh ${CMAKE_CURRENT_BINARY_DIR}
+    )
+set_tests_properties(LibWebText PROPERTIES ENVIRONMENT QT_QPA_PLATFORM=offscreen)
 endif()

Tests/LibWeb/Text/expected/basic.txt

@@ -0,0 +1,2 @@
+Well hello
+friends!

Tests/LibWeb/Text/input/basic.html

@@ -0,0 +1,9 @@
+<div id="out"></div><script>
+    function println(s) {
+        const out = document.getElementById("out");
+        out.appendChild(document.createTextNode(s + "\n"))
+    }
+
+    println("Well hello")
+    println("friends!")
+</script>

Tests/LibWeb/Text/text_test.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+set -eo pipefail
+
+SCRIPT_DIR="$(cd -P -- "$(dirname -- "${0}")" && pwd -P)"
+LADYBIRD_BUILD_DIR="${1}"
+
+if [[ -z "${LADYBIRD_BUILD_DIR}" ]] ; then
+    echo "Provide path to the Ladybird build directory"
+    exit 1
+fi
+
+BROWSER_BINARY="./headless-browser"
+
+find "${SCRIPT_DIR}/input/" -type f -name "*.html" -print0 | while IFS= read -r -d '' input_html_path; do
+    input_html_file=${input_html_path/${SCRIPT_DIR}"/input/"/}
+    input_html_file=${input_html_file/".html"/}
+
+    output_text_dump=$(cd "${LADYBIRD_BUILD_DIR}"; timeout 300s "${BROWSER_BINARY}" --dump-text "${input_html_path}")
+    expected_text_dump_path="${SCRIPT_DIR}/expected/${input_html_file}.txt"
+
+    if cmp <(echo "${output_text_dump}") "${expected_text_dump_path}"; then
+        echo "${input_html_file} PASSED"
+    else
+        echo "${input_html_file} FAILED"
+        diff -u "${expected_text_dump_path}" <(echo "${output_text_dump}")
+    fi
+done