add tests module snippet

Signed-off-by: Benjamin Coenen <5719034+bnjjj@users.noreply.github.com>

crates/ra_ide/src/completion/complete_snippet.rs

@@ -135,6 +135,14 @@ mod tests {
                 kind: Snippet,
                 lookup: "tfn",
             },
+            CompletionItem {
+                label: "Test module",
+                source_range: 78..78,
+                delete: 78..78,
+                insert: "#[cfg(test)]\nmod tests {\n    use super::*;\n\n    #[test]\n    fn ${1:test_name}() {\n        $0\n    }\n}",
+                kind: Snippet,
+                lookup: "tmod",
+            },
             CompletionItem {
                 label: "macro_rules",
                 source_range: 78..78,