feat(contracts): add testutils Cargo feature flag (#203)

Introduce a testutils feature in contracts/Cargo.toml that gates
soroban-sdk test helpers behind an explicit feature flag, keeping them
out of the production WASM binary.

Changes:
- contracts/Cargo.toml: add [features] section with
  testutils = ["soroban-sdk/testutils"]
- contracts/src/lib.rs: gate mod test with
  #[cfg(any(test, feature = "testutils"))] so the test module is
  only compiled when running tests or when the feature is explicitly
  requested
- .github/workflows/contracts-ci.yml:
  - run cargo test --features testutils so tests can use SDK mocks
  - build release WASM with --no-default-features (no testutils)
  - add verification step that asserts testutils symbols are absent
    from the release binary

Closes #203

Author: OsejiFabian

.github/workflows/contracts-ci.yml

@@ -58,11 +58,28 @@ jobs:
 
       - name: Run contract tests
         working-directory: contracts
-        run: cargo test
+        run: cargo test --features testutils
 
-      - name: Build WASM release binary
+      - name: Build WASM release binary (no testutils)
         working-directory: contracts
-        run: cargo build --target wasm32-unknown-unknown --release
+        run: cargo build --target wasm32-unknown-unknown --release --no-default-features
+
+      - name: Verify testutils excluded from release binary
+        working-directory: contracts
+        run: |
+          WASM_FILE=$(find target/wasm32-unknown-unknown/release -name "*.wasm" | head -1)
+          if [ -z "$WASM_FILE" ]; then
+            echo "ERROR: No WASM file found." >&2
+            exit 1
+          fi
+          # Confirm the strings "testutils" or "register_stellar_asset" do not
+          # appear in the release binary (they would only be present if test
+          # utilities were compiled in).
+          if strings "$WASM_FILE" | grep -qE "testutils|register_stellar_asset"; then
+            echo "ERROR: Release binary contains test utility symbols. Ensure testutils feature is excluded from release builds." >&2
+            exit 1
+          fi
+          echo "✅ Release binary does not contain test utility symbols."
 
       - name: Report WASM binary size
         working-directory: contracts

contracts/Cargo.toml

@@ -6,6 +6,15 @@ edition = "2021"
 [lib]
 crate-type = ["cdylib"]
 
+# Feature flags
+# ------------
+# `testutils` – enables soroban-sdk's test helpers (mock ledger, StellarAssetClient,
+#   Address::generate, etc.).  This feature MUST NOT be enabled for production/release
+#   WASM builds; it is only activated during `cargo test` (via dev-dependencies) and
+#   when explicitly requested with `--features testutils`.
+[features]
+testutils = ["soroban-sdk/testutils"]
+
 [dependencies]
 soroban-sdk = "21.0.0"
 

contracts/src/lib.rs

@@ -429,5 +429,5 @@ fn read_campaign(env: &Env, campaign_id: u64) -> Campaign {
         .get(&DataKey::Campaign(campaign_id))
         .unwrap_or_else(|| panic!("campaign not found"))
 }
-#[cfg(test)]
+#[cfg(any(test, feature = "testutils"))]
 mod test;