Add tests

crates/macro/ui-tests/link-to.rs

@@ -0,0 +1,24 @@
+fn good1() -> String {
+    wasm_bindgen::link_to!(inline_js = "console.log('Hello world!');")
+}
+
+fn good2() -> String {
+    wasm_bindgen::link_to!(raw_module = "package/foo.js")
+}
+
+fn bad1() -> String {
+    wasm_bindgen::link_to!(module = "/src/not-found.js")
+}
+
+fn bad2() -> String {
+    wasm_bindgen::link_to!()
+}
+
+fn bad3() -> String {
+    wasm_bindgen::link_to!(
+        inline_js = "console.log('Hello world!');",
+        js_namespace = foo
+    )
+}
+
+fn main() {}

crates/macro/ui-tests/link-to.stderr

@@ -0,0 +1,19 @@
+error: failed to read file `$WORKSPACE/target/tests/wasm-bindgen-macro/src/not-found.js`: No such file or directory (os error 2)
+  --> $DIR/link-to.rs:10:37
+   |
+10 |     wasm_bindgen::link_to!(module = "/src/not-found.js")
+   |                                     ^^^^^^^^^^^^^^^^^^^
+
+error: `link_to!` requires a module.
+  --> $DIR/link-to.rs:14:5
+   |
+14 |     wasm_bindgen::link_to!()
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in the macro `wasm_bindgen::link_to` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unused #[wasm_bindgen] attribute
+  --> $DIR/link-to.rs:20:9
+   |
+20 |         js_namespace = foo
+   |         ^^^^^^^^^^^^