diff --git a/Tests/varLib/varStore_test.py b/Tests/varLib/varStore_test.py
new file mode 100644
index 000000000..631d70100
--- /dev/null
+++ b/Tests/varLib/varStore_test.py
@@ -0,0 +1,60 @@
+import pytest
+from fontTools.varLib.models import VariationModel
+from fontTools.varLib.varStore import OnlineVarStoreBuilder, VarStoreInstancer
+from fontTools.ttLib.tables._f_v_a_r import Axis
+
+
+@pytest.mark.parametrize(
+    "locations, masterValues",
+    [
+        (
+            [{}, {"a": 1}],
+            [
+                [10, 20],
+                [100, 2000],
+                [100, 22000],
+            ],
+        ),
+        (
+            [{}, {"a": 1}, {"b": 1}, {"a": 1, "b": 1}],
+            [
+                [10, 20, 40, 60],
+                [100, 2000, 400, 6000],
+                [100, 22000, 4000, 30000],
+            ],
+        ),
+    ],
+)
+def test_onlineVarStoreBuilder(locations, masterValues):
+    axisTags = sorted({k for loc in locations for k in loc})
+    model = VariationModel(locations)
+    builder = OnlineVarStoreBuilder(axisTags)
+    builder.setModel(model)
+    expectedDeltasAndVarIdxs = []
+    for masters in masterValues:
+        base, *deltas = model.getDeltas(masters)
+        varIdx = builder.storeDeltas(deltas)
+        expectedDeltasAndVarIdxs.append((deltas, varIdx))
+
+    varStore = builder.finish()
+    varData = varStore.VarData
+
+    for deltas, varIdx in expectedDeltasAndVarIdxs:
+        major, minor = varIdx >> 16, varIdx & 0xFFFF
+        storedDeltas = varData[major].Item[minor]
+        assert deltas == storedDeltas
+
+    fvarAxes = [buildAxis(axisTag) for axisTag in axisTags]
+    instancer = VarStoreInstancer(varStore, fvarAxes)
+    for masters, (deltas, varIdx) in zip(masterValues, expectedDeltasAndVarIdxs):
+        base, *rest = masters
+        for expectedValue, loc in zip(masters, locations):
+            instancer.setLocation(loc)
+            value = base + instancer[varIdx]
+            assert expectedValue == value
+
+
+def buildAxis(axisTag):
+    axis = Axis()
+    axis.axisTag = axisTag
+    return axis