diff --git a/Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/elm/executing/FunctionRefEvaluatorTest.java b/Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/elm/executing/FunctionRefEvaluatorTest.java
new file mode 100644
index 000000000..177445e00
--- /dev/null
+++ b/Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/elm/executing/FunctionRefEvaluatorTest.java
@@ -0,0 +1,66 @@
+package org.opencds.cqf.cql.engine.elm.executing;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.Arrays;
+import java.util.List;
+import javax.xml.namespace.QName;
+import org.hl7.elm.r1.*;
+import org.junit.jupiter.api.Test;
+import org.opencds.cqf.cql.engine.exception.CqlException;
+import org.opencds.cqf.cql.engine.execution.Environment;
+import org.opencds.cqf.cql.engine.execution.State;
+
+class FunctionRefEvaluatorTest {
+    @Test
+    void pickFunctionDef() {
+        var env = new Environment(null);
+        var state = new State(env);
+        state.init(new Library().withIdentifier(new VersionedIdentifier().withId("lib")));
+
+        var cqlException = assertThrows(
+                CqlException.class,
+                () -> FunctionRefEvaluator.pickFunctionDef(state, "func", List.of(1, 2, 3), List.of(), List.of()));
+        assertEquals(
+                "Could not resolve call to operator 'func(java.lang.Integer, java.lang.Integer, java.lang.Integer)' in library 'lib'.",
+                cqlException.getMessage());
+    }
+
+    @Test
+    void functionDefOperandsSignatureEqual() {
+        var functionDefWithOneOperand = new FunctionDef().withOperand(new OperandDef());
+        List<TypeSpecifier> signatureWithTwoOperands = List.of(new NamedTypeSpecifier(), new NamedTypeSpecifier());
+
+        assertFalse(FunctionRefEvaluator.functionDefOperandsSignatureEqual(
+                functionDefWithOneOperand, signatureWithTwoOperands));
+    }
+
+    @Test
+    void operandDefTypeSpecifierEqual() {
+        var integerTypeName = new QName("urn:hl7-org:elm-types:r1", "Integer");
+        var integerNamedTypeSpecifier = new NamedTypeSpecifier().withName(integerTypeName);
+        var listTypeSpecifier = new ListTypeSpecifier().withElementType(integerNamedTypeSpecifier);
+
+        var listOperandDef = new OperandDef().withOperandTypeSpecifier(listTypeSpecifier);
+        var integerOperandDef = new OperandDef().withOperandType(integerTypeName);
+
+        assertTrue(FunctionRefEvaluator.operandDefTypeSpecifierEqual(listOperandDef, listTypeSpecifier));
+        assertTrue(FunctionRefEvaluator.operandDefTypeSpecifierEqual(integerOperandDef, integerNamedTypeSpecifier));
+        assertFalse(FunctionRefEvaluator.operandDefTypeSpecifierEqual(integerOperandDef, null));
+    }
+
+    @Test
+    void typesToString() {
+        var env = new Environment(null);
+        var state = new State(env);
+
+        var actual = FunctionRefEvaluator.typesToString(state, List.of("a", "b", "c"));
+        assertEquals("java.lang.String, java.lang.String, java.lang.String", actual);
+
+        actual = FunctionRefEvaluator.typesToString(state, Arrays.asList(1, 2, null));
+        assertEquals("java.lang.Integer, java.lang.Integer, null", actual);
+
+        actual = FunctionRefEvaluator.typesToString(state, null);
+        assertEquals("", actual);
+    }
+}