Add handy message for how to diff manually instead of using meld since (

apache#18)

it's hard to install meld on mac. Also, wget may be missing on mac so
auto-install that during automatic spark-download.

Fix the first-regtest-setup case by updating SPARK_HOME after download.

regtests/run.sh

@@ -58,7 +58,8 @@ for TEST_FILE in ${TEST_LIST}; do
     echo '#!/bin/bash' > ${TEST_TMPDIR}/${TEST_SHORTNAME}.fixdiffs.sh
     echo "meld ${TEST_STDOUT} ${TEST_REF}" >> ${TEST_TMPDIR}/${TEST_SHORTNAME}.fixdiffs.sh
     chmod 750 ${TEST_TMPDIR}/${TEST_SHORTNAME}.fixdiffs.sh
-    logred "To compare and fix diffs: ${TEST_TMPDIR}/${TEST_SHORTNAME}.fixdiffs.sh"
+    logred "To compare and fix diffs (if 'meld' installed): ${TEST_TMPDIR}/${TEST_SHORTNAME}.fixdiffs.sh"
+    logred "Or manually diff: diff ${TEST_STDOUT} ${TEST_REF}"
     logred "See stderr from test run for additional diagnostics: ${TEST_STDERR}"
     NUM_FAILURES=$(( NUM_FAILURES + 1 ))
   fi

regtests/setup.sh

@@ -10,18 +10,28 @@ set -x
 SPARK_HOME=$(realpath ~/spark-3.5.1-bin-hadoop3-scala2.13)
 SPARK_CONF="${SPARK_HOME}/conf/spark-defaults.conf"
 
+
 # Ensure binaries are downloaded locally
 echo 'Verifying Spark binaries...'
 if ! [ -f ${SPARK_HOME}/bin/spark-sql ]; then
   echo 'Setting up Spark...'
   if ! [ -f ~/spark-3.5.1-bin-hadoop3-scala2.13.tgz ]; then
     echo 'Downloading spark distro...'
     wget -O ~/spark-3.5.1-bin-hadoop3-scala2.13.tgz https://dlcdn.apache.org/spark/spark-3.5.1/spark-3.5.1-bin-hadoop3-scala2.13.tgz
+    if ! [ -f ~/spark-3.5.1-bin-hadoop3-scala2.13.tgz ]; then
+      if [[ "${OSTYPE}" == "darwin"* ]]; then
+        echo "Detected OS: mac. Running 'brew install wget' to try again."
+        brew install wget
+        wget -O ~/spark-3.5.1-bin-hadoop3-scala2.13.tgz https://dlcdn.apache.org/spark/spark-3.5.1/spark-3.5.1-bin-hadoop3-scala2.13.tgz
+      fi
+    fi
   else
     echo 'Found existing Spark tarball'
   fi
   tar xzvf ~/spark-3.5.1-bin-hadoop3-scala2.13.tgz -C ~
   echo 'Done!'
+  SPARK_HOME=$(realpath ~/spark-3.5.1-bin-hadoop3-scala2.13)
+  SPARK_CONF="${SPARK_HOME}/conf/spark-defaults.conf"
 else
   echo 'Verified Spark distro already installed.'
 fi