Add tiny crate for better predicate assertions

Author: ian-h-chamberlain

testutils/.gitignore

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+Cargo.lock
+target/

testutils/Cargo.toml

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+[package]
+name = "testutils"
+version = "0.1.0"
+authors = ["Ian Chamberlain <[email protected]>"]
+edition = "2018"
+
+[dependencies]
+predicates = "1.0.2"
+predicates-tree = "1.0.0"

testutils/src/lib.rs

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+/// Simple macro to panic with a prettier error message
+/// # Examples
+/// ```
+/// use predicates::prelude::*;
+/// use testutils::assert_that;
+///
+/// assert_that!(
+///     "Hello World",
+///     predicates::str::similar("Hello World"),
+/// );
+/// assert_that!(
+///     "Hello world",
+///     predicates::str::diff("Goodbye world"),
+/// );
+/// ```
+#[macro_export]
+macro_rules! assert_that {
+    ($item:expr, $pred:expr $(,)?) => {{
+        use ::predicates::prelude::*;
+        use ::predicates_tree::CaseTreeExt;
+
+        if let Some(case) = $pred.find_case(false, $item) {
+            panic!("{}", case.tree());
+        };
+    }};
+}