Make the gtest macro compatible with no_std crates.

The code emitted by the gtest macro now references Result from
the core crate rather than the std crate. Avoiding the reference
to the std crate makes the resulting code no_std compatible.

The Result struct was moved from std to core in Rust v1.6.0, which
is part of the Rust 2018 edition.

Author: carlwhamilton

googletest/tests/no_std_test.rs

@@ -0,0 +1,37 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#![no_std]
+
+/// A simple, no_std function.
+fn no_std_identity(value: u32) -> u32 {
+    value
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use googletest::prelude::*;
+
+    #[gtest]
+    fn no_std_verify() -> Result<()> {
+        verify_eq!(no_std_identity(42), 42)?;
+        Ok(())
+    }
+
+    #[gtest]
+    fn no_std_expect() {
+        expect_eq!(no_std_identity(214), 214)
+    }
+}

googletest_macro/src/lib.rs

@@ -105,7 +105,7 @@ pub fn gtest(
         .unwrap_or_else(||
         (
             quote! {Ok(())},
-            quote! { ::std::result::Result<(), googletest::internal::test_outcome::TestFailure> },
+            quote! { ::core::result::Result<(), googletest::internal::test_outcome::TestFailure> },
             quote! {},
         ));