Implement an assertor for anyhow error

Cargo.toml

@@ -15,9 +15,10 @@ categories = ["development-tools::testing", "development-tools::debugging"]
 
 [dependencies]
 num-traits = { version = "0.2.15", optional = true }
+anyhow = { version = "1.0.86", optional = true }
 
 [features]
 default = ["float"]
-float = ["num-traits"]
+float = ["dep:num-traits"]
 testing = []
-
+anyhow = ["dep:anyhow"]

README.md

@@ -53,6 +53,31 @@ fn test_it() {
 }
 ```
 
+## anyhow
+
+Supports asserting error value of `anyhow` under `anyhow` feature flag.
+
+```toml
+[dependencies]
+assertor = { version = "*", features = ["anyhow"] }
+```
+
+```rust
+use assertor::*;
+use anyhow::anyhow;
+
+fn anyhow_func() -> anyhow::Result<()> {
+    Err(anyhow!("failed to parse something in foobar"))
+}
+
+fn test_it() {
+    assert_that!(anyhow_func()).err().has_message("failed to parse something in foobar");
+    assert_that!(anyhow_func()).err().as_string().contains("parse something");
+    assert_that!(anyhow_func()).err().as_string().starts_with("failed");
+    assert_that!(anyhow_func()).err().as_string().ends_with("foobar");
+}
+```
+
 ## Feature ideas
 
 - [ ] Color / Bold

src/assertions/anyhow.rs

@@ -0,0 +1,118 @@
+// Copyright 2024 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.
+
+
+use crate::base::{AssertionApi, AssertionResult, AssertionStrategy, Subject};
+use crate::StringAssertion;
+
+/// Trait for anyhow error assertion.
+///
+/// # Example
+///
+/// ```rust
+/// use assertor::*;
+/// use anyhow::anyhow;
+///
+/// fn anyhow_func() -> anyhow::Result<()> {
+///     Err(anyhow!("failed to parse something in foobar"))
+/// }
+///
+/// fn test_it() {
+///     assert_that!(anyhow_func()).err().has_message("failed to parse something in foobar");
+///     assert_that!(anyhow_func()).err().as_string().contains("parse something");
+///     assert_that!(anyhow_func()).err().as_string().starts_with("failed");
+///     assert_that!(anyhow_func()).err().as_string().ends_with("foobar");
+/// }
+/// ```
+pub trait AnyhowErrorAssertion<R> {
+    /// Returns a new `String` subject which is the message of the error.
+    ///
+    /// Related: [`StringAssertion`](crate::StringAssertion)
+    ///
+    /// ```
+    /// use assertor::*;
+    /// use anyhow::anyhow;
+    ///
+    /// assert_that!(anyhow!("error message")).as_string().is_same_string_to("error message");
+    /// assert_that!(anyhow!("error message")).as_string().contains("error");
+    ///
+    ///
+    /// fn some_func() -> anyhow::Result<()> {
+    ///    Err(anyhow!("error message"))
+    /// }
+    /// assert_that!(some_func()).err().as_string().starts_with("error");
+    /// assert_that!(some_func()).err().as_string().ends_with("message");
+    /// ```
+    fn as_string(&self) -> Subject<String, (), R>;
+
+    /// Checks that the error message contains `expected`.
+    /// ```
+    /// use assertor::*;
+    /// use anyhow::anyhow;
+    ///
+    /// assert_that!(anyhow!("error message")).has_message("error message");
+    ///
+    /// fn some_func() -> anyhow::Result<()> {
+    ///    Err(anyhow!("error message"))
+    /// }
+    /// assert_that!(some_func()).err().has_message("error message")
+    /// ```
+    fn has_message<E: Into<String>>(&self, expected: E) -> R;
+}
+
+impl<R> AnyhowErrorAssertion<R> for Subject<'_, anyhow::Error, (), R>
+    where
+        AssertionResult: AssertionStrategy<R>,
+{
+    fn as_string(&self) -> Subject<String, (), R> {
+        let message = self.actual().to_string();
+        self.new_owned_subject(message, Some(format!("{}.to_string()", self.description_or_expr())), ())
+    }
+
+    fn has_message<E: Into<String>>(&self, expected: E) -> R {
+        self.as_string().is_same_string_to(expected)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::testing::*;
+
+    use super::*;
+
+    #[test]
+    fn as_string() {
+        assert_that!(anyhow::Error::msg("error message")).as_string().is_same_string_to("error message");
+        assert_that!(anyhow::Error::msg("error message")).as_string().starts_with("error");
+        assert_that!(anyhow::Error::msg("error message")).as_string().contains("or");
+
+        assert_that!(check_that!(anyhow::Error::msg("error message")).as_string().is_same_string_to("wrong")).facts_are(
+            vec![
+                Fact::new("expected", "\"wrong\""),
+                Fact::new("actual", "\"error message\""),
+            ]
+        );
+    }
+
+    #[test]
+    fn has_message() {
+        assert_that!(anyhow::Error::msg("error message")).has_message("error message");
+        assert_that!(check_that!(anyhow::Error::msg("error message")).has_message("wrong")).facts_are(
+            vec![
+                Fact::new("expected", "\"wrong\""),
+                Fact::new("actual", "\"error message\""),
+            ]
+        );
+    }
+}

src/assertions/mod.rs

@@ -25,5 +25,8 @@ pub mod vec;
 #[cfg(feature = "float")]
 pub mod float;
 
+#[cfg(feature = "anyhow")]
+pub mod anyhow;
+
 #[cfg(any(test, doc, feature = "testing"))]
 pub(crate) mod testing;

src/assertions/result.rs

@@ -15,6 +15,7 @@
 use std::borrow::Borrow;
 use std::fmt::Debug;
 
+use crate::assert_that;
 use crate::base::{AssertionApi, AssertionResult, AssertionStrategy, Subject};
 
 /// Trait for result assertion.
@@ -40,18 +41,24 @@ pub trait ResultAssertion<R, OK, ERR> {
 
     /// Checks that the subject is [`Result::Ok(expected)`](`std::result::Result::Err`).
     fn has_ok<B: Borrow<OK>>(&self, expected: B) -> R
-    where
-        OK: PartialEq;
+        where
+            OK: PartialEq;
 
     /// Checks that the subject is [`Result::Err(expected)`](`std::result::Result::Err`).
     fn has_err<B: Borrow<ERR>>(&self, expected: B) -> R
-    where
-        ERR: PartialEq;
+        where
+            ERR: PartialEq;
+
+    /// Returns a new subject which is the ok value of the subject if the subject has ok value. Otherwise, it fails.
+    fn ok(&self) -> Subject<OK, (), R>;
+
+    /// Returns a new subject which is the error value of the subject if the subject has error value. Otherwise, it fails. 
+    fn err(&self) -> Subject<ERR, (), R>;
 }
 
 impl<R, OK: Debug, ERR: Debug> ResultAssertion<R, OK, ERR> for Subject<'_, Result<OK, ERR>, (), R>
-where
-    AssertionResult: AssertionStrategy<R>,
+    where
+        AssertionResult: AssertionStrategy<R>,
 {
     fn is_ok(&self) -> R {
         if self.actual().is_ok() {
@@ -80,8 +87,8 @@ where
     }
 
     fn has_ok<B: Borrow<OK>>(&self, expected: B) -> R
-    where
-        OK: PartialEq,
+        where
+            OK: PartialEq,
     {
         match self.actual() {
             Ok(actual) if actual.eq(expected.borrow()) => self.new_result().do_ok(),
@@ -99,8 +106,8 @@ where
     }
 
     fn has_err<B: Borrow<ERR>>(&self, expected: B) -> R
-    where
-        ERR: PartialEq,
+        where
+            ERR: PartialEq,
     {
         match self.actual() {
             Err(actual) if actual.eq(expected.borrow()) => self.new_result().do_ok(),
@@ -116,10 +123,21 @@ where
                 .do_fail(),
         }
     }
+
+    fn ok(&self) -> Subject<OK, (), R> {
+        assert_that!(*self.actual()).is_ok();
+        self.new_subject(self.actual().as_ref().ok().unwrap(), Some(format!("{}.ok", self.description_or_expr())), ())
+    }
+
+    fn err(&self) -> Subject<ERR, (), R> {
+        assert_that!(*self.actual()).is_err();
+        self.new_subject(self.actual().as_ref().err().unwrap(), Some(format!("{}.err", self.description_or_expr())), ())
+    }
 }
 
 #[cfg(test)]
 mod tests {
+    use crate::ComparableAssertion;
     use crate::testing::*;
 
     use super::*;
@@ -189,4 +207,26 @@ mod tests {
             ],
         );
     }
+
+    #[test]
+    fn ok() {
+        assert_that!(Result::<f64,()>::Ok(0.)).ok().is_at_most(1.);
+    }
+
+    #[test]
+    #[should_panic]
+    fn ok_panic() {
+        assert_that!(Result::<f64,()>::Err(())).ok().is_at_most(1.);
+    }
+
+    #[test]
+    fn err() {
+        assert_that!(Result::<(), f64>::Err(0.)).err().is_at_most(1.);
+    }
+
+    #[test]
+    #[should_panic]
+    fn err_panic() {
+        assert_that!(Result::<(), f64>::Ok(())).err().is_at_most(1.);
+    }
 }

src/lib.rs

@@ -47,6 +47,8 @@
 #[cfg(feature = "float")]
 extern crate num_traits;
 
+#[cfg(feature = "anyhow")]
+pub use assertions::anyhow::AnyhowErrorAssertion;
 pub use assertions::basic::{ComparableAssertion, EqualityAssertion};
 pub use assertions::boolean::BooleanAssertion;
 #[cfg(feature = "float")]