diff --git a/crates/ra_db/src/fixture.rs b/crates/ra_db/src/fixture.rs
index ee883b6154..ade187629b 100644
--- a/crates/ra_db/src/fixture.rs
+++ b/crates/ra_db/src/fixture.rs
@@ -8,8 +8,8 @@ use rustc_hash::FxHashMap;
 use test_utils::{extract_offset, parse_fixture, CURSOR_MARKER};
 
 use crate::{
-    CrateGraph, Edition, FileId, FilePosition, RelativePathBuf, SourceDatabaseExt, SourceRoot,
-    SourceRootId,
+    CrateGraph, CrateId, Edition, FileId, FilePosition, RelativePathBuf, SourceDatabaseExt,
+    SourceRoot, SourceRootId,
 };
 
 pub const WORKSPACE: SourceRootId = SourceRootId(0);
@@ -33,6 +33,14 @@ pub trait WithFixture: Default + SourceDatabaseExt + 'static {
         let pos = with_files(&mut db, fixture);
         (db, pos.unwrap())
     }
+
+    fn test_crate(&self) -> CrateId {
+        let crate_graph = self.crate_graph();
+        let mut it = crate_graph.iter();
+        let res = it.next().unwrap();
+        assert!(it.next().is_none());
+        res
+    }
 }
 
 impl<DB: SourceDatabaseExt + Default + 'static> WithFixture for DB {}
diff --git a/crates/ra_hir_def/src/nameres/collector.rs b/crates/ra_hir_def/src/nameres/collector.rs
index 37d0f30936..83eef821f7 100644
--- a/crates/ra_hir_def/src/nameres/collector.rs
+++ b/crates/ra_hir_def/src/nameres/collector.rs
@@ -798,7 +798,7 @@ mod tests {
 
     fn do_limited_resolve(code: &str, limit: u32, poison_limit: u32) -> CrateDefMap {
         let (db, _file_id) = TestDB::with_single_file(&code);
-        let krate = db.crate_graph().iter().next().unwrap();
+        let krate = db.test_crate();
 
         let def_map = {
             let edition = db.crate_graph().edition(krate);
diff --git a/crates/ra_hir_def/src/nameres/tests/incremental.rs b/crates/ra_hir_def/src/nameres/tests/incremental.rs
index 80dcec62f0..903a227719 100644
--- a/crates/ra_hir_def/src/nameres/tests/incremental.rs
+++ b/crates/ra_hir_def/src/nameres/tests/incremental.rs
@@ -1,12 +1,12 @@
 use std::sync::Arc;
 
-use ra_db::{SourceDatabase, SourceDatabaseExt};
+use ra_db::SourceDatabaseExt;
 
 use super::*;
 
 fn check_def_map_is_not_recomputed(initial: &str, file_change: &str) {
     let (mut db, pos) = TestDB::with_position(initial);
-    let krate = db.crate_graph().iter().next().unwrap();
+    let krate = db.test_crate();
     {
         let events = db.log_executed(|| {
             db.crate_def_map(krate);
@@ -111,7 +111,7 @@ fn typing_inside_a_macro_should_not_invalidate_def_map() {
         m!(X);
         ",
     );
-    let krate = db.crate_graph().iter().next().unwrap();
+    let krate = db.test_crate();
     {
         let events = db.log_executed(|| {
             let crate_def_map = db.crate_def_map(krate);
diff --git a/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs b/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs
index dee364a142..eb7b85c07c 100644
--- a/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs
+++ b/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs
@@ -656,7 +656,7 @@ fn unresolved_module_diagnostics() {
         //- /foo.rs
         ",
     );
-    let krate = db.crate_graph().iter().next().unwrap();
+    let krate = db.test_crate();
 
     let crate_def_map = db.crate_def_map(krate);