Shareable function for partitioning integration tests (#17223)

For the fedramp high work https://github.com/elastic/logstash/pull/17038/files a
use case for multiple scripts consuming the partitioning functionality emerged.
As we look to more advanced partitioning we want to ensure that the
functionality will be consumable from multiple scripts.

See #17219 (comment)

Author: donoghuc

ci/get-test-half.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+# get_test_half returns either the first or second half of integration tests
+# Usage: get_test_half <half_number>
+# half_number: 0 for first half, 1 for second half
+get_test_half() {
+    local half_number=$1
+    # Ensure only spec files go to stdout
+    pushd qa/integration >/dev/null 2>&1
+    
+    # Collect all spec files
+    local glob1=(specs/*spec.rb)
+    local glob2=(specs/**/*spec.rb)
+    local all_specs=("${glob1[@]}" "${glob2[@]}")
+    
+    # Calculate the split point
+    local split_point=$((${#all_specs[@]} / 2))
+    
+    # Get the requested half (:: is "up to", : is "from")
+    if [[ $half_number -eq 0 ]]; then
+        local specs="${all_specs[@]::$split_point}"
+    else
+        local specs="${all_specs[@]:$split_point}"
+    fi
+    popd >/dev/null 2>&1
+    echo "$specs"
+}

ci/integration_tests.sh

@@ -10,6 +10,9 @@ export GRADLE_OPTS="-Xmx2g -Dorg.gradle.jvmargs=-Xmx2g -Dorg.gradle.daemon=false
 export SPEC_OPTS="--order rand --format documentation"
 export CI=true
 
+# Source shared function for splitting integration tests
+source "$(dirname "${BASH_SOURCE[0]}")/get-test-half.sh"
+
 if [ -n "$BUILD_JAVA_HOME" ]; then
   GRADLE_OPTS="$GRADLE_OPTS -Dorg.gradle.java.home=$BUILD_JAVA_HOME"
 fi
@@ -19,20 +22,10 @@ if [[ $1 = "setup" ]]; then
  exit 0
 
 elif [[ $1 == "split" ]]; then
-    cd qa/integration
-    glob1=(specs/*spec.rb)
-    glob2=(specs/**/*spec.rb)
-    all_specs=("${glob1[@]}" "${glob2[@]}")
-
-    specs0=${all_specs[@]::$((${#all_specs[@]} / 2 ))}
-    specs1=${all_specs[@]:$((${#all_specs[@]} / 2 ))}
-    cd ../..
-    if [[ $2 == 0 ]]; then
-       echo "Running the first half of integration specs: $specs0"
-       ./gradlew runIntegrationTests -PrubyIntegrationSpecs="$specs0" --console=plain
-    elif [[ $2 == 1 ]]; then
-       echo "Running the second half of integration specs: $specs1"
-       ./gradlew runIntegrationTests -PrubyIntegrationSpecs="$specs1" --console=plain
+    if [[ $2 =~ ^[01]$ ]]; then
+        specs=$(get_test_half "$2")
+        echo "Running half $2 of integration specs: $specs"
+        ./gradlew runIntegrationTests -PrubyIntegrationSpecs="$specs" --console=plain
     else
        echo "Error, must specify 0 or 1 after the split. For example ci/integration_tests.sh split 0"
        exit 1