Fix macOS CI by installing gcc for gfortran

.github/workflows/build.yml

@@ -29,7 +29,11 @@ jobs:
         os:
           - ubuntu-latest
           - windows-latest
-          - macos-latest
+          # Pinned: Homebrew bottles on macos-latest (macOS 26) carry
+          # minos 26.0, which delocate rejects against the 15.0 wheel
+          # target below. Keep this image and MACOSX_DEPLOYMENT_TARGET
+          # in sync if either changes.
+          - macos-15
 
     steps:
       - name: Checkout source
@@ -42,9 +46,12 @@ jobs:
         with:
           python-version: "3.12"
 
-      - name: Add gforran to PATH (macOS)
+      - name: Install gfortran (macOS)
         if: runner.os == 'macOS'
-        run: echo "$(brew --prefix gcc)/bin" >> "$GITHUB_PATH"
+        run: |
+          brew install gcc || brew link --overwrite gcc
+          echo "$(brew --prefix gcc)/bin" >> "$GITHUB_PATH"
+          "$(brew --prefix gcc)/bin/gfortran" --version
 
       - name: Install MinGW via Chocolatey (Windows)
         if: runner.os == 'Windows'

.github/workflows/release-pypi.yml

@@ -23,7 +23,11 @@ jobs:
         os:
           - ubuntu-latest
           - windows-latest
-          - macos-latest
+          # Pinned: Homebrew bottles on macos-latest (macOS 26) carry
+          # minos 26.0, which delocate rejects against the 15.0 wheel
+          # target below. Keep this image and MACOSX_DEPLOYMENT_TARGET
+          # in sync if either changes.
+          - macos-15
 
     steps:
       - name: Checkout source
@@ -37,9 +41,12 @@ jobs:
         with:
           python-version: "3.12"
 
-      - name: Add gfortran to PATH (macOS)
+      - name: Install gfortran (macOS)
         if: runner.os == 'macOS'
-        run: echo "$(brew --prefix gcc)/bin" >> "$GITHUB_PATH"
+        run: |
+          brew install gcc || brew link --overwrite gcc
+          echo "$(brew --prefix gcc)/bin" >> "$GITHUB_PATH"
+          "$(brew --prefix gcc)/bin/gfortran" --version
 
       - name: Install Python dependencies
         run: |

.github/workflows/test.yml

@@ -42,17 +42,22 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest]
+        # macos pinned to 15 to match the wheel target used in build.yml
+        # and release-pypi.yml; see the note there.
+        os: [ubuntu-latest, windows-latest, macos-15]
         python-version: ${{ fromJson(needs.fetch-python-versions.outputs.supported_versions) }}
 
     steps:
       - uses: actions/checkout@v7
         with:
           fetch-depth: 0
 
-      - name: Add gfortran to PATH (macOS)
+      - name: Install gfortran (macOS)
         if: runner.os == 'macOS'
-        run: echo "$(brew --prefix gcc)/bin" >> "$GITHUB_PATH"
+        run: |
+          brew install gcc || brew link --overwrite gcc
+          echo "$(brew --prefix gcc)/bin" >> "$GITHUB_PATH"
+          "$(brew --prefix gcc)/bin/gfortran" --version
 
       - name: Install MinGW via Chocolatey (Windows)
         if: runner.os == 'Windows'

tests/test_banana_no_constraints.py

@@ -13,7 +13,9 @@ def banana_func(x: NDArray[np.floating]) -> np.floating:
 def test_banana_no_constraints() -> None:
     lb = [-3, -1]
     ub = [2, 6]
-    result = pso(banana_func, lb, ub, debug=True)
+    # Seeded: PSO is stochastic, and unseeded this assertion fails on
+    # roughly 1 in 75 runs at atol=0.001.
+    result = pso(banana_func, lb, ub, debug=True, seed=2)
     xopt, fopt = result.x, result.fun
     if not np.allclose(xopt, [1.0, 1.0], atol=0.001):
         msg = f"Expected xopt close to [1.0, 1.0], got {xopt}"

tests/test_banana_with_constraints.py

@@ -19,7 +19,9 @@ def banana_constraint(x: NDArray[np.floating]) -> list[float]:
 def test_banana_with_constraints() -> None:
     lb = [-3, -1]
     ub = [2, 6]
-    result = pso(banana_func, lb, ub, f_ieqcons=banana_constraint, debug=True)
+    result = pso(
+        banana_func, lb, ub, f_ieqcons=banana_constraint, debug=True, seed=2
+    )
     xopt, fopt = result.x, result.fun
     if not np.allclose(xopt, [0.5, 0.75], atol=0.1):
         msg = f"Expected xopt close to [0.5, 0.75], got {xopt}"