Add std as required feature for tests

.github/workflows/rust.yml

@@ -10,10 +10,13 @@ jobs:
     strategy:
       matrix:
         rust: ["1.34.2", stable, beta, nightly]
-        features: [ "", "std" ]
+        features: ["", "std"]
     steps:
     - uses: actions/checkout@v2
-    - run: rustup default ${{ matrix.rust }}
+    - uses: actions-rs/toolchain@v1
+      with:
+        toolchain: ${{ matrix.rust }}
+        override: true
     - name: build
       run: >
         cargo build --verbose --no-default-features --features "$FEATURES"

Cargo.toml

@@ -30,6 +30,19 @@ raii_no_panic = []
 # Reservation for a feature turning off std
 std = []
 
+[[test]]
+name = "check_testimages"
+required-features = ["std"]
+
+[[test]]
+name = "decode"
+required-features = ["std"]
+
+[[test]]
+name = "roundtrip"
+required-features = ["std"]
+
 [[bench]]
 name = "decode"
 harness = false
+required-features = ["std"]