Move mixed format input test to integration

The test was specified using snapshot tests, which aren't really a good
fit for multiple input files. While it worked locally, it didn't work on
the CI, where it couldn't find the input files, despite efforts to
properly set the current working directory in the test process. In the
end, it was simpler to move it to a manual intergration test, which is a
bit more cumbersome but more flexible.

Author: yannham

cli/tests/snapshot/imports/mixed.json renamed to cli/tests/integration/inputs/mixed.json

@@ -1,5 +1,7 @@
 use std::{
+    ffi::OsString,
     io::Write,
+    path::PathBuf,
     process::{Command, Stdio},
 };
 
@@ -73,3 +75,60 @@ fn automatic_color_on_non_tty() {
         );
     }
 }
+
+#[test]
+// This test didn't fit the snapshot test specification very well. While it can be encoded as
+// snapshot test, it didn't work on the CI (where the working directory doesn't seem to be properly
+// set for some reason), so we are using a manual test for now.
+fn merge_mixed_formats() {
+    // Provide a current directory-independent path to the input files of integration tests.
+    fn input_path(name: &str) -> OsString {
+        let mut path = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+        path.push("tests/integration/inputs");
+        path.push(name);
+        path.into_os_string()
+    }
+
+    let nickel_bin = env!("CARGO_BIN_EXE_nickel");
+
+    let nickel = Command::new(nickel_bin)
+        .arg("export")
+        .args([
+            input_path("mixed.ncl"),
+            input_path("mixed.json"),
+            input_path("mixed.toml"),
+        ])
+        .arg("--apply-contract")
+        .arg(input_path("mixed_contract.ncl"))
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .expect("Nickel should be runnable");
+
+    let output = nickel
+        .wait_with_output()
+        .expect("couldn't retrieve stdout handle to Nickel");
+
+    let stderr_output =
+        String::from_utf8(output.stderr).expect("The result of Nickel should be valid utf8");
+    let stdout_output =
+        String::from_utf8(output.stdout).expect("The result of Nickel should be valid utf8");
+
+    assert_eq!(stderr_output, "");
+    assert_eq!(
+        stdout_output,
+        "\
+{
+  \"bar\": 123,
+  \"extra\": {
+    \"json\": true,
+    \"nickel\": true,
+    \"subfield\": \"here\",
+    \"toml\": true
+  },
+  \"foo\": \"hello\"
+}
+"
+    );
+}