make tests pass on Windows

Also add CI for Windows.

.github/workflows/rust.yml

@@ -11,8 +11,11 @@ env:
 
 jobs:
   build:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest]
 
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v2

Cargo.toml

@@ -14,3 +14,6 @@ all-features = true
 
 [dependencies]
 camino = { version = "1.0.5", optional = true }
+
+[dev-dependencies]
+cfg-if = "1.0.0"

src/lib.rs

@@ -152,12 +152,24 @@ pub use crate::utf8_paths::*;
 #[cfg(test)]
 mod tests {
     use super::*;
+    use cfg_if::cfg_if;
 
     #[test]
     fn test_absolute() {
-        assert_diff_paths("/foo", "/bar", Some("../foo"));
-        assert_diff_paths("/foo", "bar", Some("/foo"));
-        assert_diff_paths("foo", "/bar", None);
+        fn abs(path: &str) -> String {
+            // Absolute paths look different on Windows vs Unix.
+            cfg_if! {
+                if #[cfg(windows)] {
+                    format!("C:\\{}", path)
+                } else {
+                    format!("/{}", path)
+                }
+            }
+        }
+
+        assert_diff_paths(&abs("foo"), &abs("bar"), Some("../foo"));
+        assert_diff_paths(&abs("foo"), "bar", Some(&abs("foo")));
+        assert_diff_paths("foo", &abs("bar"), None);
         assert_diff_paths("foo", "bar", Some("../foo"));
     }