diff --git a/mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h b/mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h
--- a/mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h
+++ b/mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h
@@ -230,6 +230,10 @@
     return tensor(b) == outTensor && index(b) == i;
   }
 
+  /// Gets tensor ID for special tensors
+  unsigned getOutTensorID() const { return outTensor; }
+  unsigned getSynTensorID() const { return syntheticTensor; }
+
   /// Returns true if given tensor iterates *only* in the given tensor
   /// expression. For the output tensor, this defines a "simply dynamic"
   /// operation [Bik96]. For instance: a(i) *= 2.0 or a(i) += a(i) for
diff --git a/mlir/unittests/Dialect/SparseTensor/MergerTest.cpp b/mlir/unittests/Dialect/SparseTensor/MergerTest.cpp
--- a/mlir/unittests/Dialect/SparseTensor/MergerTest.cpp
+++ b/mlir/unittests/Dialect/SparseTensor/MergerTest.cpp
@@ -309,6 +309,8 @@
   const unsigned l0 = 0;
 
   MergerTest3T1L() : MergerTestBase(3, 1) {
+    EXPECT_TRUE(merger.getOutTensorID() == t2);
+
     // Tensor 0: sparse input vector.
     merger.addExp(Kind::kTensor, t0, -1u);
     merger.setDimLevelType(t0, l0, DimLevelType::Compressed);
@@ -332,6 +334,8 @@
   const unsigned l0 = 0;
 
   MergerTest4T1L() : MergerTestBase(4, 1) {
+    EXPECT_TRUE(merger.getOutTensorID() == t3);
+
     // Tensor 0: sparse input vector.
     merger.addExp(Kind::kTensor, t0, -1u);
     merger.setDimLevelType(t0, l0, DimLevelType::Compressed);
@@ -363,6 +367,8 @@
   const unsigned l0 = 0;
 
   MergerTest3T1LD() : MergerTestBase(3, 1) {
+    EXPECT_TRUE(merger.getOutTensorID() == t2);
+
     // Tensor 0: sparse input vector.
     merger.addExp(Kind::kTensor, t0, -1u);
     merger.setDimLevelType(t0, l0, DimLevelType::Compressed);
@@ -383,13 +389,15 @@
 
 class MergerTest4T1LU : public MergerTestBase {
 protected:
-  // Our three tensors (two inputs, one output).
+  // Our three tensors (three inputs, one output).
   const unsigned t0 = 0, t1 = 1, t2 = 2, t3 = 3;
 
   // Our single loop.
   const unsigned l0 = 0;
 
   MergerTest4T1LU() : MergerTestBase(4, 1) {
+    EXPECT_TRUE(merger.getOutTensorID() == t3);
+
     // Tensor 0: undef input vector.
     merger.addExp(Kind::kTensor, t0, -1u);
     merger.setDimLevelType(t0, l0, DimLevelType::Undef);
@@ -421,6 +429,9 @@
   const unsigned l0 = 0;
 
   MergerTest3T1L_SO() : MergerTestBase(3, 1) {
+    EXPECT_TRUE(merger.getOutTensorID() == t2);
+    EXPECT_TRUE(merger.getSynTensorID() == t3);
+
     merger.setHasSparseOut(true);
 
     // Tensor 0: undef input vector.