From d56b637c373957c15a55b6d0e292bbd04ad9c124 Mon Sep 17 00:00:00 2001
From: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Date: Tue, 21 Jul 2026 20:41:48 -0400
Subject: [PATCH 1/2] Preserve downgraded old-style test extras

Keep floor-resolved test extras reachable through build and Pkg.test, while preserving source/no-promote exclusions and restoring each Project.toml byte-for-byte. Add cross-version sandbox, cleanup, and workflow synchronization coverage.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
---
 .github/workflows/downgrade.yml            | 107 ++++++++++
 .github/workflows/sublibrary-downgrade.yml | 105 ++++++++++
 README.md                                  |  16 ++
 test/runtests.jl                           | 228 +++++++++++++++++++++
 4 files changed, 456 insertions(+)

diff --git a/.github/workflows/downgrade.yml b/.github/workflows/downgrade.yml
index a90d823..f57743a 100644
--- a/.github/workflows/downgrade.yml
+++ b/.github/workflows/downgrade.yml
@@ -129,6 +129,105 @@ jobs:
           mode: "${{ inputs.mode != '' && inputs.mode || 'deps' }}"
           no_promote: "${{ inputs.no_promote }}"
 
+      - name: "Keep resolved test extras reachable during build and test"
+        env:
+          DOWNGRADE_TEST_PROJECT: "${{ inputs.project }}"
+          DOWNGRADE_NO_PROMOTE: "${{ inputs.no_promote }}"
+        run: |
+          project_dir="$DOWNGRADE_TEST_PROJECT"
+          [ "$project_dir" = "@." ] && project_dir="."
+          case "$project_dir" in
+            @*) echo "Project must be a directory path or @.: $project_dir" >&2; exit 1 ;;
+          esac
+          project_file=""
+          for filename in Project.toml JuliaProject.toml; do
+            candidate="$project_dir/$filename"
+            if [ -f "$candidate" ]; then project_file="$candidate"; break; fi
+          done
+          [ -n "$project_file" ] || { echo "No Project.toml or JuliaProject.toml in $project_dir" >&2; exit 1; }
+          backup="$RUNNER_TEMP/sciml-downgrade-original-project.toml"
+          cp -- "$project_file" "$backup"
+          echo "DOWNGRADE_PROJECT_FILE=$project_file" >> "$GITHUB_ENV"
+          echo "DOWNGRADE_PROJECT_BACKUP=$backup" >> "$GITHUB_ENV"
+          julia --startup-file=no - "$DOWNGRADE_TEST_PROJECT" "$DOWNGRADE_NO_PROMOTE" <<'JULIA'
+          using TOML
+
+          function project_file(project::AbstractString)
+              directory = project == "@." ? "." : project
+              startswith(directory, "@") &&
+                  error("project must be a directory path or @., got: $project")
+              for filename in ("Project.toml", "JuliaProject.toml")
+                  candidate = joinpath(directory, filename)
+                  isfile(candidate) && return candidate
+              end
+              error("no Project.toml or JuliaProject.toml in $directory")
+          end
+
+          function write_project(path::AbstractString, project::AbstractDict)
+              temporary, io = mktemp(dirname(path))
+              try
+                  TOML.print(io, project)
+                  close(io)
+                  mv(temporary, path; force = true)
+              catch
+                  isopen(io) && close(io)
+                  ispath(temporary) && rm(temporary; force = true)
+                  rethrow()
+              end
+              return nothing
+          end
+
+          function promote_test_extras(project::AbstractString, no_promote = String[])
+              path = project_file(project)
+              parsed = TOML.parsefile(path)
+              extras = get(parsed, "extras", Dict{String, Any}())
+              targets = get(parsed, "targets", Dict{String, Any}())
+              test_target = get(targets, "test", String[])
+              test_target isa AbstractVector || error("[targets].test must be an array in $path")
+              excluded = Set(strip.(filter(!isempty, no_promote)))
+              sources = Set(keys(get(parsed, "sources", Dict{String, Any}())))
+              names = sort!(unique!(String.(test_target)))
+              deps = get(parsed, "deps", Dict{String, Any}())
+              for name in names
+                  if haskey(extras, name) && haskey(deps, name) && deps[name] != extras[name]
+                      error("$name has different UUIDs in [deps] and [extras] in $path")
+                  end
+              end
+              targeted_extras = filter(name -> haskey(extras, name), names)
+              skipped_no_promote = filter(name -> name ∈ excluded, targeted_extras)
+              skipped_sources = filter(name -> name ∈ sources, targeted_extras)
+              promoted = filter(names) do name
+                  haskey(extras, name) && !haskey(deps, name) &&
+                      name ∉ excluded && name ∉ sources
+              end
+              @info "Selected old-style test extras for the downgraded environment" project = path promoted skipped_no_promote skipped_sources
+              isempty(promoted) && return promoted
+
+              deps = get!(parsed, "deps", Dict{String, Any}())
+              weakdeps = get(parsed, "weakdeps", nothing)
+              for name in promoted
+                  uuid = extras[name]
+                  deps[name] = uuid
+                  weakdeps isa AbstractDict && delete!(weakdeps, name)
+              end
+              weakdeps isa AbstractDict && isempty(weakdeps) && delete!(parsed, "weakdeps")
+              write_project(path, parsed)
+              @info "Promoted resolved test extras into [deps]" project = path promoted
+              return promoted
+          end
+
+          function main(args)
+              length(args) == 2 || error("usage: promote_test_extras.jl PROJECT NO_PROMOTE")
+              no_promote = filter(!isempty, strip.(split(args[2], ',')))
+              promote_test_extras(args[1], no_promote)
+              return nothing
+          end
+
+          if PROGRAM_FILE == "-" || abspath(PROGRAM_FILE) == @__FILE__
+              main(ARGS)
+          end
+          JULIA
+
       - name: "Install system packages"
         if: "${{ inputs.apt-packages != '' && runner.os == 'Linux' }}"
         run: |
@@ -150,3 +249,11 @@ jobs:
           force_latest_compatible_version: false
         env:
           GROUP: "${{ inputs.group }}"
+
+      - name: "Restore the original project file"
+        if: ${{ always() }}
+        run: |
+          if [ -n "${DOWNGRADE_PROJECT_BACKUP:-}" ] && [ -f "$DOWNGRADE_PROJECT_BACKUP" ]; then
+            cp -- "$DOWNGRADE_PROJECT_BACKUP" "$DOWNGRADE_PROJECT_FILE"
+            rm -- "$DOWNGRADE_PROJECT_BACKUP"
+          fi
diff --git a/.github/workflows/sublibrary-downgrade.yml b/.github/workflows/sublibrary-downgrade.yml
index 5c5174c..d7efdb9 100644
--- a/.github/workflows/sublibrary-downgrade.yml
+++ b/.github/workflows/sublibrary-downgrade.yml
@@ -172,6 +172,104 @@ jobs:
           projects: ${{ matrix.project }}
           skip: ${{ env.EFFECTIVE_SKIP }}
           julia_version: ${{ env.JULIA_MM }}
+      - name: "Keep resolved test extras reachable during build and test"
+        env:
+          DOWNGRADE_TEST_PROJECT: ${{ matrix.project }}
+          DOWNGRADE_NO_PROMOTE: ""
+        run: |
+          project_dir="$DOWNGRADE_TEST_PROJECT"
+          [ "$project_dir" = "@." ] && project_dir="."
+          case "$project_dir" in
+            @*) echo "Project must be a directory path or @.: $project_dir" >&2; exit 1 ;;
+          esac
+          project_file=""
+          for filename in Project.toml JuliaProject.toml; do
+            candidate="$project_dir/$filename"
+            if [ -f "$candidate" ]; then project_file="$candidate"; break; fi
+          done
+          [ -n "$project_file" ] || { echo "No Project.toml or JuliaProject.toml in $project_dir" >&2; exit 1; }
+          backup="$RUNNER_TEMP/sciml-downgrade-original-project.toml"
+          cp -- "$project_file" "$backup"
+          echo "DOWNGRADE_PROJECT_FILE=$project_file" >> "$GITHUB_ENV"
+          echo "DOWNGRADE_PROJECT_BACKUP=$backup" >> "$GITHUB_ENV"
+          julia --startup-file=no - "$DOWNGRADE_TEST_PROJECT" "$DOWNGRADE_NO_PROMOTE" <<'JULIA'
+          using TOML
+
+          function project_file(project::AbstractString)
+              directory = project == "@." ? "." : project
+              startswith(directory, "@") &&
+                  error("project must be a directory path or @., got: $project")
+              for filename in ("Project.toml", "JuliaProject.toml")
+                  candidate = joinpath(directory, filename)
+                  isfile(candidate) && return candidate
+              end
+              error("no Project.toml or JuliaProject.toml in $directory")
+          end
+
+          function write_project(path::AbstractString, project::AbstractDict)
+              temporary, io = mktemp(dirname(path))
+              try
+                  TOML.print(io, project)
+                  close(io)
+                  mv(temporary, path; force = true)
+              catch
+                  isopen(io) && close(io)
+                  ispath(temporary) && rm(temporary; force = true)
+                  rethrow()
+              end
+              return nothing
+          end
+
+          function promote_test_extras(project::AbstractString, no_promote = String[])
+              path = project_file(project)
+              parsed = TOML.parsefile(path)
+              extras = get(parsed, "extras", Dict{String, Any}())
+              targets = get(parsed, "targets", Dict{String, Any}())
+              test_target = get(targets, "test", String[])
+              test_target isa AbstractVector || error("[targets].test must be an array in $path")
+              excluded = Set(strip.(filter(!isempty, no_promote)))
+              sources = Set(keys(get(parsed, "sources", Dict{String, Any}())))
+              names = sort!(unique!(String.(test_target)))
+              deps = get(parsed, "deps", Dict{String, Any}())
+              for name in names
+                  if haskey(extras, name) && haskey(deps, name) && deps[name] != extras[name]
+                      error("$name has different UUIDs in [deps] and [extras] in $path")
+                  end
+              end
+              targeted_extras = filter(name -> haskey(extras, name), names)
+              skipped_no_promote = filter(name -> name ∈ excluded, targeted_extras)
+              skipped_sources = filter(name -> name ∈ sources, targeted_extras)
+              promoted = filter(names) do name
+                  haskey(extras, name) && !haskey(deps, name) &&
+                      name ∉ excluded && name ∉ sources
+              end
+              @info "Selected old-style test extras for the downgraded environment" project = path promoted skipped_no_promote skipped_sources
+              isempty(promoted) && return promoted
+
+              deps = get!(parsed, "deps", Dict{String, Any}())
+              weakdeps = get(parsed, "weakdeps", nothing)
+              for name in promoted
+                  uuid = extras[name]
+                  deps[name] = uuid
+                  weakdeps isa AbstractDict && delete!(weakdeps, name)
+              end
+              weakdeps isa AbstractDict && isempty(weakdeps) && delete!(parsed, "weakdeps")
+              write_project(path, parsed)
+              @info "Promoted resolved test extras into [deps]" project = path promoted
+              return promoted
+          end
+
+          function main(args)
+              length(args) == 2 || error("usage: promote_test_extras.jl PROJECT NO_PROMOTE")
+              no_promote = filter(!isempty, strip.(split(args[2], ',')))
+              promote_test_extras(args[1], no_promote)
+              return nothing
+          end
+
+          if PROGRAM_FILE == "-" || abspath(PROGRAM_FILE) == @__FILE__
+              main(ARGS)
+          end
+          JULIA
       - name: "Install system packages"
         if: "${{ inputs.apt-packages != '' && runner.os == 'Linux' }}"
         run: |
@@ -184,3 +282,10 @@ jobs:
         with:
           project: ${{ matrix.project }}
           allow_reresolve: false
+      - name: "Restore the original project file"
+        if: ${{ always() }}
+        run: |
+          if [ -n "${DOWNGRADE_PROJECT_BACKUP:-}" ] && [ -f "$DOWNGRADE_PROJECT_BACKUP" ]; then
+            cp -- "$DOWNGRADE_PROJECT_BACKUP" "$DOWNGRADE_PROJECT_FILE"
+            rm -- "$DOWNGRADE_PROJECT_BACKUP"
+          fi
diff --git a/README.md b/README.md
index 7116328..e7a480d 100644
--- a/README.md
+++ b/README.md
@@ -259,6 +259,8 @@ to catch under-specified `[compat]` lower bounds.
 | `skip` | string | `""` | **Additional** deps to skip when downgrading, beyond the auto-included Julia stdlibs and any `[sources]` path/url deps (see note). |
 | `projects` | string | `"."` | Comma-separated project dirs to downgrade. |
 | `project` | string | `"@."` | `--project` for build/test (a workspace submodule or `lib/X`); default tests the repo root. |
+| `mode` | string | `"deps"` | Dependency set minimized by `julia-downgrade-compat`: `deps`, `alldeps`, `weakdeps`, or `forcedeps`. |
+| `no_promote` | string | `"Mooncake"` | Comma-separated old-style test extras left out of the joint floor resolve. |
 | `self-hosted` / `os` | | `false` / `ubuntu-latest` | Runner selection. |
 | `apt-packages` | string | `""` | Space-separated apt packages to install before building/testing (Linux only). |
 | `container` | string | `""` | Docker container image to run the job in (e.g. `cmhyett/julia-fenics:latest` for Python-stack packages). Empty = no container. |
@@ -282,6 +284,14 @@ jobs:
 > [SciML/.github #73](https://github.com/SciML/.github/pull/73); strict
 > `allow_reresolve: false` is already in effect.)
 
+For old-style `[extras]` / `[targets].test` dependencies, the workflow
+temporarily adds each floor-resolved test extra to the active project's
+`[deps]` before build and test. This keeps `Pkg.test` from replacing an orphaned
+manifest floor with the newest compatible version. `[sources]` and
+`no_promote` entries are left untouched, new-style `test/Project.toml`
+environments keep their existing handling, and an `always()` cleanup restores
+the original project file byte-for-byte.
+
 ### `documentation.yml`
 
 Builds and deploys [Documenter](https://documenter.juliadocs.org/)
@@ -780,6 +790,12 @@ jobs:
 > [SciML/.github #73](https://github.com/SciML/.github/pull/73); strict
 > `allow_reresolve: false` is already in effect.)
 
+Old-style `[extras]` / `[targets].test` dependencies are temporarily added to
+the sublibrary's `[deps]` after floor resolution so `Pkg.build` and `Pkg.test`
+retain those exact manifest versions. Source-backed extras are not rewritten,
+new-style `test/Project.toml` environments keep their existing handling, and
+an `always()` cleanup restores the original project file byte-for-byte.
+
 ---
 
 ## Recommended repository setup
diff --git a/test/runtests.jl b/test/runtests.jl
index 67fba1a..fc5d094 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,4 +1,5 @@
 using Test
+using TOML
 
 # Load the detection script's functions without running main().
 const SCRIPT = joinpath(@__DIR__, "..", "scripts", "compute_affected_sublibraries.jl")
@@ -592,3 +593,230 @@ end
     root = make_sources_fixture()
     @test isempty(collect_source_paths(joinpath(root, "Leaf")))
 end
+
+function embedded_promote_test_extras(path)
+    lines = readlines(path)
+    first_line = findfirst(line -> occursin("<<'JULIA'", line), lines)
+    first_line === nothing && error("no Julia heredoc in $path")
+    last_line = findnext(line -> strip(line) == "JULIA", lines, first_line + 1)
+    last_line === nothing && error("unterminated Julia heredoc in $path")
+    source = map(lines[(first_line + 1):(last_line - 1)]) do line
+        startswith(line, "          ") ? line[11:end] : line
+    end
+    return join(source, '\n') * '\n'
+end
+
+const PROMOTE_TEST_EXTRAS_SOURCE = embedded_promote_test_extras(
+    joinpath(@__DIR__, "..", ".github", "workflows", "downgrade.yml")
+)
+include_string(Main, PROMOTE_TEST_EXTRAS_SOURCE, "embedded promote_test_extras.jl")
+
+@testset "promote_test_extras production source stays synchronized" begin
+    workflows = ("downgrade.yml", "sublibrary-downgrade.yml")
+    for workflow in workflows
+        path = joinpath(@__DIR__, "..", ".github", "workflows", workflow)
+        text = read(path, String)
+        @test embedded_promote_test_extras(path) == PROMOTE_TEST_EXTRAS_SOURCE
+        @test occursin("cp -- \"\$project_file\" \"\$backup\"", text)
+        @test occursin("cp -- \"\$DOWNGRADE_PROJECT_BACKUP\" \"\$DOWNGRADE_PROJECT_FILE\"", text)
+        @test occursin(raw"if: ${{ always() }}", text)
+        resolve_at = findfirst("julia-actions/julia-downgrade-compat", text)
+        promote_at = findfirst("Keep resolved test extras reachable", text)
+        build_at = findfirst("julia-actions/julia-buildpkg", text)
+        test_at = findfirst("julia-actions/julia-runtest", text)
+        restore_at = findfirst("Restore the original project file", text)
+        @test all(!isnothing, (resolve_at, promote_at, build_at, test_at, restore_at))
+        @test first(resolve_at) < first(promote_at) < first(build_at) < first(test_at) <
+            first(restore_at)
+    end
+end
+
+@testset "promote_test_extras selects only resolved old-style test dependencies" begin
+    root = mktempdir()
+    project_path = joinpath(root, "Project.toml")
+    original = """
+    name = "PromotionFixture"
+    uuid = "00000000-0000-0000-0000-000000000001"
+
+    [deps]
+    Existing = "00000000-0000-0000-0000-000000000002"
+
+    [weakdeps]
+    PromotedWeak = "00000000-0000-0000-0000-000000000003"
+    UntargetedWeak = "00000000-0000-0000-0000-000000000004"
+
+    [extras]
+    PromotedPure = "00000000-0000-0000-0000-000000000005"
+    PromotedWeak = "00000000-0000-0000-0000-000000000003"
+    Excluded = "00000000-0000-0000-0000-000000000006"
+    SourceExtra = "00000000-0000-0000-0000-000000000007"
+    NotTargeted = "00000000-0000-0000-0000-000000000008"
+
+    [sources]
+    SourceExtra = {path = "../SourceExtra"}
+
+    [targets]
+    test = ["PromotedPure", "PromotedWeak", "Excluded", "SourceExtra"]
+    """
+    write(project_path, original)
+
+    promoted = promote_test_extras(root, ["Excluded"])
+    project = TOML.parsefile(project_path)
+    @test promoted == ["PromotedPure", "PromotedWeak"]
+    @test project["deps"]["PromotedPure"] == project["extras"]["PromotedPure"]
+    @test project["deps"]["PromotedWeak"] == project["extras"]["PromotedWeak"]
+    @test !haskey(project["deps"], "Excluded")
+    @test !haskey(project["deps"], "SourceExtra")
+    @test !haskey(project["deps"], "NotTargeted")
+    @test !haskey(project["weakdeps"], "PromotedWeak")
+    @test haskey(project["weakdeps"], "UntargetedWeak")
+    @test promote_test_extras(root, ["Excluded"]) == String[]
+end
+
+@testset "promote_test_extras keeps no-op projects byte-identical" begin
+    root = mktempdir()
+    project_path = joinpath(root, "JuliaProject.toml")
+    original = """
+    name = "NoPromotionFixture"
+    uuid = "00000000-0000-0000-0000-000000000010"
+
+    [extras]
+    NotTargeted = "00000000-0000-0000-0000-000000000011"
+
+    [targets]
+    test = []
+    """
+    write(project_path, original)
+    cd(root) do
+        @test promote_test_extras("@.") == String[]
+    end
+    @test read(project_path, String) == original
+end
+
+@testset "promote_test_extras leaves new-style test environments untouched" begin
+    root = mktempdir()
+    project = joinpath(root, "lib", "NewStyleFixture")
+    test_directory = joinpath(project, "test")
+    mkpath(test_directory)
+    root_project = """
+    name = "NewStyleFixture"
+    uuid = "00000000-0000-0000-0000-000000000012"
+
+    [deps]
+    RuntimeDep = "00000000-0000-0000-0000-000000000013"
+    """
+    test_project = """
+    [deps]
+    TestDep = "00000000-0000-0000-0000-000000000014"
+    """
+    write(joinpath(project, "Project.toml"), root_project)
+    write(joinpath(test_directory, "Project.toml"), test_project)
+
+    @test promote_test_extras(project) == String[]
+    @test read(joinpath(project, "Project.toml"), String) == root_project
+    @test read(joinpath(test_directory, "Project.toml"), String) == test_project
+end
+
+function with_project_backup(f, project_path, backup_path)
+    cp(project_path, backup_path; force = true)
+    try
+        return f()
+    finally
+        cp(backup_path, project_path; force = true)
+        rm(backup_path; force = true)
+    end
+end
+
+@testset "project backup restores exact bytes after success and failure" begin
+    for fail in (false, true)
+        root = mktempdir()
+        project_path = joinpath(root, "Project.toml")
+        backup_path = joinpath(root, "original.toml")
+        original = """
+        # This comment and ordering must survive cleanup exactly.
+        name = "RestoreFixture"
+        uuid = "00000000-0000-0000-0000-000000000015"
+
+        [extras]
+        TestDep = "00000000-0000-0000-0000-000000000016"
+
+        [targets]
+        test = ["TestDep"]
+        """
+        write(project_path, original)
+        operation = () -> with_project_backup(project_path, backup_path) do
+            @test promote_test_extras(root) == ["TestDep"]
+            @test read(project_path, String) != original
+            fail && error("restore failure-path fixture")
+        end
+        fail ? (@test_throws ErrorException operation()) : operation()
+        @test read(project_path, String) == original
+        @test !isfile(backup_path)
+    end
+end
+
+@testset "promoted test extras survive the Pkg.test sandbox" begin
+    root = mktempdir()
+    package = joinpath(root, "PromotionPkg")
+    dependency = joinpath(root, "FloorFixtureDep")
+    mkpath(joinpath(package, "src"))
+    mkpath(joinpath(package, "test"))
+    mkpath(joinpath(dependency, "src"))
+    write(
+        joinpath(package, "Project.toml"),
+        """
+        name = "PromotionPkg"
+        uuid = "00000000-0000-0000-0000-000000000020"
+        version = "0.1.0"
+
+        [extras]
+        FloorFixtureDep = "00000000-0000-0000-0000-000000000021"
+
+        [targets]
+        test = ["FloorFixtureDep"]
+
+        [compat]
+        FloorFixtureDep = "0.1, 0.2"
+        julia = "1.10"
+        """
+    )
+    manifest_path = joinpath(package, "Manifest.toml")
+    write(
+        manifest_path,
+        """
+        julia_version = "$(VERSION)"
+        manifest_format = "2.0"
+
+        [[deps.FloorFixtureDep]]
+        path = "../FloorFixtureDep"
+        uuid = "00000000-0000-0000-0000-000000000021"
+        version = "0.1.0"
+        """
+    )
+    write(joinpath(package, "src", "PromotionPkg.jl"), "module PromotionPkg\nend\n")
+    write(
+        joinpath(package, "test", "runtests.jl"),
+        "using FloorFixtureDep\n@assert FloorFixtureDep.VERSION_MARKER == v\"0.1.0\"\n"
+    )
+    write(
+        joinpath(dependency, "Project.toml"),
+        """
+        name = "FloorFixtureDep"
+        uuid = "00000000-0000-0000-0000-000000000021"
+        version = "0.1.0"
+        """
+    )
+    write(
+        joinpath(dependency, "src", "FloorFixtureDep.jl"),
+        "module FloorFixtureDep\nconst VERSION_MARKER = v\"0.1.0\"\nend\n"
+    )
+
+    @test promote_test_extras(package) == ["FloorFixtureDep"]
+    locked_manifest = read(manifest_path)
+    julia = joinpath(Sys.BINDIR, "julia" * (Sys.iswindows() ? ".exe" : ""))
+    command = `$julia --startup-file=no --project=$package -e 'using Pkg; Pkg.build(; verbose=true); Pkg.test(; allow_reresolve=false)'`
+    @test success(pipeline(command; stdout, stderr))
+    @test read(manifest_path) == locked_manifest
+    manifest = TOML.parsefile(manifest_path)
+    @test manifest["deps"]["FloorFixtureDep"][1]["version"] == "0.1.0"
+end

From 4d16630091d8a7c4397f0fe3653d88beaad7b15c Mon Sep 17 00:00:00 2001
From: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Date: Tue, 21 Jul 2026 22:14:34 -0400
Subject: [PATCH 2/2] Preserve package default test group

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
---
 .github/workflows/downgrade.yml |  8 ++++++--
 test/runtests.jl                | 15 +++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/downgrade.yml b/.github/workflows/downgrade.yml
index f57743a..f6adb73 100644
--- a/.github/workflows/downgrade.yml
+++ b/.github/workflows/downgrade.yml
@@ -238,6 +238,12 @@ jobs:
         with:
           project: "${{ inputs.project }}"
 
+      - name: "Export requested test group"
+        if: "${{ inputs.group != '' }}"
+        env:
+          REQUESTED_GROUP: "${{ inputs.group }}"
+        run: printf 'GROUP=%s\n' "$REQUESTED_GROUP" >> "$GITHUB_ENV"
+
       - uses: julia-actions/julia-runtest@v1
         with:
           project: "${{ inputs.project }}"
@@ -247,8 +253,6 @@ jobs:
           # and fails resolution (e.g. "empty intersection between X@min and project
           # compatibility latest"). Downgrade tests must keep the minimum versions.
           force_latest_compatible_version: false
-        env:
-          GROUP: "${{ inputs.group }}"
 
       - name: "Restore the original project file"
         if: ${{ always() }}
diff --git a/test/runtests.jl b/test/runtests.jl
index fc5d094..f7124ec 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -631,6 +631,21 @@ include_string(Main, PROMOTE_TEST_EXTRAS_SOURCE, "embedded promote_test_extras.j
     end
 end
 
+@testset "empty downgrade group preserves the package default" begin
+    path = joinpath(@__DIR__, "..", ".github", "workflows", "downgrade.yml")
+    text = read(path, String)
+    export_at = findfirst("Export requested test group", text)
+    test_at = findfirst("julia-actions/julia-runtest", text)
+    @test all(!isnothing, (export_at, test_at))
+    @test first(export_at) < first(test_at)
+    @test occursin(raw"if: \"${{ inputs.group != '' }}\"", text)
+    @test occursin(raw"REQUESTED_GROUP: \"${{ inputs.group }}\"", text)
+    @test occursin(raw"run: printf 'GROUP=%s\n' \"$REQUESTED_GROUP\" >> \"$GITHUB_ENV\"", text)
+    @test !any(
+        line -> strip(line) == raw"GROUP: \"${{ inputs.group }}\"", eachline(IOBuffer(text))
+    )
+end
+
 @testset "promote_test_extras selects only resolved old-style test dependencies" begin
     root = mktempdir()
     project_path = joinpath(root, "Project.toml")