Add tests for bad format syntax

Author: andrewhickman

tests/fmt_missing_arg.rs

@@ -0,0 +1,8 @@
+use fn_error_context::error_context;
+
+#[error_context("{}")]
+fn do_stuff() -> anyhow::Result<()> {
+    anyhow::bail!("error")
+}
+
+fn main() {}

tests/fmt_missing_arg.stderr

@@ -0,0 +1,5 @@
+error: 1 positional argument in format string, but no arguments were given
+ --> $DIR/fmt_missing_arg.rs:3:18
+  |
+3 | #[error_context("{}")]
+  |                  ^^

tests/fmt_unused_arg.rs

@@ -0,0 +1,8 @@
+use fn_error_context::error_context;
+
+#[error_context("context", 1)]
+fn do_stuff() -> anyhow::Result<()> {
+    anyhow::bail!("error")
+}
+
+fn main() {}

tests/fmt_unused_arg.stderr

@@ -0,0 +1,7 @@
+error: argument never used
+ --> $DIR/fmt_unused_arg.rs:3:28
+  |
+3 | #[error_context("context", 1)]
+  |                 ---------  ^ argument never used
+  |                 |
+  |                 formatting specifier missing

tests/tests.rs

@@ -12,4 +12,6 @@ fn tests() {
     tests.pass("tests/non_copy_arg.rs");
     tests.pass("tests/non_copy_fmt_arg.rs");
     tests.pass("tests/as_ref.rs");
+    tests.compile_fail("tests/fmt_missing_arg.rs");
+    tests.compile_fail("tests/fmt_unused_arg.rs");
 }