diff --git a/tests/gc/db.rs b/tests/gc/db.rs
new file mode 100644
index 00000000..5883ebfd
--- /dev/null
+++ b/tests/gc/db.rs
@@ -0,0 +1,26 @@
+use crate::group;
+
+#[derive(Default)]
+pub struct DatabaseImpl {
+    runtime: salsa::Runtime<DatabaseImpl>,
+}
+
+impl salsa::Database for DatabaseImpl {
+    fn salsa_runtime(&self) -> &salsa::Runtime<DatabaseImpl> {
+        &self.runtime
+    }
+}
+
+salsa::database_storage! {
+    pub struct DatabaseImplStorage for DatabaseImpl {
+        impl group::GcDatabase {
+            fn min() for group::Min;
+            fn max() for group::Max;
+            fn use_triangular() for group::UseTriangular;
+            fn fibonacci() for group::Fibonacci;
+            fn triangular() for group::Triangular;
+            fn compute() for group::Compute;
+            fn compute_all() for group::ComputeAll;
+        }
+    }
+}
diff --git a/tests/gc/group.rs b/tests/gc/group.rs
new file mode 100644
index 00000000..9be5f9e2
--- /dev/null
+++ b/tests/gc/group.rs
@@ -0,0 +1,64 @@
+salsa::query_group! {
+    pub(crate) trait GcDatabase: salsa::Database {
+        fn min() -> usize {
+            type Min;
+            storage input;
+        }
+
+        fn max() -> usize {
+            type Max;
+            storage input;
+        }
+
+        fn use_triangular(key: usize) -> bool {
+            type UseTriangular;
+            storage input;
+        }
+
+        fn fibonacci(key: usize) -> usize {
+            type Fibonacci;
+        }
+
+        fn triangular(key: usize) -> usize {
+            type Triangular;
+        }
+
+        fn compute(key: usize) -> usize {
+            type Compute;
+        }
+
+        fn compute_all() -> Vec<usize> {
+            type ComputeAll;
+        }
+    }
+}
+
+fn fibonacci(db: &impl GcDatabase, key: usize) -> usize {
+    if key == 0 {
+        0
+    } else if key == 1 {
+        1
+    } else {
+        db.fibonacci(key - 1) + db.fibonacci(key - 2)
+    }
+}
+
+fn triangular(db: &impl GcDatabase, key: usize) -> usize {
+    if key == 0 {
+        0
+    } else {
+        db.triangular(key - 1) + key
+    }
+}
+
+fn compute(db: &impl GcDatabase, key: usize) -> usize {
+    if db.use_triangular(key) {
+        db.triangular(key)
+    } else {
+        db.fibonacci(key)
+    }
+}
+
+fn compute_all(db: &impl GcDatabase) -> Vec<usize> {
+    (db.min()..db.max()).map(|v| db.compute(v)).collect()
+}
diff --git a/tests/gc/main.rs b/tests/gc/main.rs
new file mode 100644
index 00000000..04300a1e
--- /dev/null
+++ b/tests/gc/main.rs
@@ -0,0 +1,4 @@
+mod db;
+mod derived_tests;
+mod group;
+mod shallow_constant_tests;
diff --git a/tests/gc/shallow_constant_tests.rs b/tests/gc/shallow_constant_tests.rs
new file mode 100644
index 00000000..bda164c3
--- /dev/null
+++ b/tests/gc/shallow_constant_tests.rs
@@ -0,0 +1,86 @@
+use crate::db;
+use crate::group::{Fibonacci, GcDatabase};
+use salsa::debug::DebugQueryTable;
+use salsa::Database;
+
+// For constant values (like `fibonacci`), we only keep the values
+// that were used in the latest revision, not the sub-values that
+// they required to be computed.
+
+#[test]
+fn one_rev() {
+    let db = db::DatabaseImpl::default();
+
+    db.fibonacci(5);
+
+    let k: Vec<_> = db.query(Fibonacci).keys();
+    assert_eq!(k.len(), 6);
+
+    // Everything was used in this revision, so
+    // nothing gets collected.
+    db.sweep_all();
+    assert_eq!(k.len(), 6);
+}
+
+#[test]
+fn two_rev_nothing() {
+    let db = db::DatabaseImpl::default();
+
+    db.fibonacci(5);
+
+    let k: Vec<_> = db.query(Fibonacci).keys();
+    assert_eq!(k.len(), 6);
+
+    db.salsa_runtime().next_revision();
+
+    // Nothing was used in this revision, so
+    // everything gets collected.
+    db.sweep_all();
+
+    let k: Vec<_> = db.query(Fibonacci).keys();
+    assert_eq!(k.len(), 0);
+}
+
+#[test]
+fn two_rev_one_use() {
+    let db = db::DatabaseImpl::default();
+
+    db.fibonacci(5);
+
+    let k: Vec<_> = db.query(Fibonacci).keys();
+    assert_eq!(k.len(), 6);
+
+    db.salsa_runtime().next_revision();
+
+    db.fibonacci(5);
+
+    // fibonacci is a constant, so it will not be invalidated,
+    // hence we keep `fibonacci(5)` but remove 0..=4.
+    db.sweep_all();
+
+    let k: Vec<_> = db.query(Fibonacci).keys();
+    assert_eq!(k, vec![5]);
+}
+
+#[test]
+fn two_rev_two_uses() {
+    let db = db::DatabaseImpl::default();
+
+    db.fibonacci(5);
+
+    let k: Vec<_> = db.query(Fibonacci).keys();
+    assert_eq!(k.len(), 6);
+
+    db.salsa_runtime().next_revision();
+
+    db.fibonacci(5);
+    db.fibonacci(3);
+
+    // fibonacci is a constant, so it will not be invalidated,
+    // hence we keep 3 and 5 but remove the rest.
+    db.sweep_all();
+
+    let mut k: Vec<_> = db.query(Fibonacci).keys();
+    k.sort();
+    assert_eq!(k, vec![3, 5]);
+}