diff --git a/lib/core/condition_tree_evaluator/index.spec.ts b/lib/core/condition_tree_evaluator/index.spec.ts
new file mode 100644
index 000000000..5afdd0d7d
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+++ b/lib/core/condition_tree_evaluator/index.spec.ts
@@ -0,0 +1,218 @@
+/**
+ * Copyright 2025, Optimizely
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import { describe, it, vi, expect } from 'vitest';
+
+import * as conditionTreeEvaluator from '.';
+
+const conditionA = {
+  name: 'browser_type',
+  value: 'safari',
+  type: 'custom_attribute',
+};
+const conditionB = {
+  name: 'device_model',
+  value: 'iphone6',
+  type: 'custom_attribute',
+};
+const conditionC = {
+  name: 'location',
+  match: 'exact',
+  type: 'custom_attribute',
+  value: 'CA',
+};
+describe('evaluate', function() {
+  it('should return true for a leaf condition when the leaf condition evaluator returns true', function() {
+    expect(
+      conditionTreeEvaluator.evaluate(conditionA, function() {
+        return true;
+      })
+    ).toBe(true);
+  });
+
+  it('should return false for a leaf condition when the leaf condition evaluator returns false', function() {
+    expect(
+      conditionTreeEvaluator.evaluate(conditionA, function() {
+        return false;
+      })
+    ).toBe(false);
+  });
+
+  describe('and evaluation', function() {
+    it('should return true when ALL conditions evaluate to true', function() {
+      expect(
+        conditionTreeEvaluator.evaluate(['and', conditionA, conditionB], function() {
+          return true;
+        })
+      ).toBe(true);
+    });
+
+    it('should return false if one condition evaluates to false', function() {
+      const leafEvaluator = vi.fn();
+      leafEvaluator.mockImplementationOnce(() => true).mockImplementationOnce(() => false);
+      expect(conditionTreeEvaluator.evaluate(['and', conditionA, conditionB], leafEvaluator)).toBe(false);
+    });
+
+    describe('null handling', function() {
+      it('should return null when all operands evaluate to null', function() {
+        expect(
+          conditionTreeEvaluator.evaluate(['and', conditionA, conditionB], function() {
+            return null;
+          })
+        ).toBeNull();
+      });
+
+      it('should return null when operands evaluate to trues and nulls', function() {
+        const leafEvaluator = vi.fn();
+        leafEvaluator.mockImplementationOnce(() => true).mockImplementationOnce(() => null);
+        expect(conditionTreeEvaluator.evaluate(['and', conditionA, conditionB], leafEvaluator)).toBeNull();
+      });
+
+      it('should return false when operands evaluate to falses and nulls', function() {
+        const leafEvaluator = vi.fn();
+        leafEvaluator.mockImplementationOnce(() => false).mockImplementationOnce(() => null);
+        expect(conditionTreeEvaluator.evaluate(['and', conditionA, conditionB], leafEvaluator)).toBe(false);
+
+        leafEvaluator.mockReset();
+        leafEvaluator.mockImplementationOnce(() => null).mockImplementationOnce(() => false);
+        expect(conditionTreeEvaluator.evaluate(['and', conditionA, conditionB], leafEvaluator)).toBe(false);
+      });
+
+      it('should return false when operands evaluate to trues, falses, and nulls', function() {
+        const leafEvaluator = vi.fn();
+        leafEvaluator
+          .mockImplementationOnce(() => true)
+          .mockImplementationOnce(() => false)
+          .mockImplementationOnce(() => null);
+        expect(conditionTreeEvaluator.evaluate(['and', conditionA, conditionB, conditionC], leafEvaluator)).toBe(false);
+      });
+    });
+  });
+
+  describe('or evaluation', function() {
+    it('should return true if any condition evaluates to true', function() {
+      const leafEvaluator = vi.fn();
+      leafEvaluator.mockImplementationOnce(() => false).mockImplementationOnce(() => true);
+      expect(conditionTreeEvaluator.evaluate(['or', conditionA, conditionB], leafEvaluator)).toBe(true);
+    });
+
+    it('should return false if all conditions evaluate to false', function() {
+      expect(
+        conditionTreeEvaluator.evaluate(['or', conditionA, conditionB], function() {
+          return false;
+        })
+      ).toBe(false);
+    });
+
+    describe('null handling', function() {
+      it('should return null when all operands evaluate to null', function() {
+        expect(
+          conditionTreeEvaluator.evaluate(['or', conditionA, conditionB], function() {
+            return null;
+          })
+        ).toBeNull();
+      });
+
+      it('should return true when operands evaluate to trues and nulls', function() {
+        const leafEvaluator = vi.fn();
+        leafEvaluator.mockImplementationOnce(() => true).mockImplementationOnce(() => null);
+        expect(conditionTreeEvaluator.evaluate(['or', conditionA, conditionB], leafEvaluator)).toBe(true);
+      });
+
+      it('should return null when operands evaluate to falses and nulls', function() {
+        const leafEvaluator = vi.fn();
+        leafEvaluator.mockImplementationOnce(() => null).mockImplementationOnce(() => false);
+        expect(conditionTreeEvaluator.evaluate(['or', conditionA, conditionB], leafEvaluator)).toBeNull();
+
+        leafEvaluator.mockReset();
+        leafEvaluator.mockImplementationOnce(() => false).mockImplementationOnce(() => null);
+        expect(conditionTreeEvaluator.evaluate(['or', conditionA, conditionB], leafEvaluator)).toBeNull();
+      });
+
+      it('should return true when operands evaluate to trues, falses, and nulls', function() {
+        const leafEvaluator = vi.fn();
+        leafEvaluator
+          .mockImplementationOnce(() => true)
+          .mockImplementationOnce(() => null)
+          .mockImplementationOnce(() => false);
+        expect(conditionTreeEvaluator.evaluate(['or', conditionA, conditionB, conditionC], leafEvaluator)).toBe(true);
+      });
+    });
+  });
+
+  describe('not evaluation', function() {
+    it('should return true if the condition evaluates to false', function() {
+      expect(
+        conditionTreeEvaluator.evaluate(['not', conditionA], function() {
+          return false;
+        })
+      ).toBe(true);
+    });
+
+    it('should return false if the condition evaluates to true', function() {
+      expect(
+        conditionTreeEvaluator.evaluate(['not', conditionB], function() {
+          return true;
+        })
+      ).toBe(false);
+    });
+
+    it('should return the result of negating the first condition, and ignore any additional conditions', function() {
+      let result = conditionTreeEvaluator.evaluate(['not', '1', '2', '1'], function(id: string) {
+        return id === '1';
+      });
+      expect(result).toBe(false);
+      result = conditionTreeEvaluator.evaluate(['not', '1', '2', '1'], function(id: string) {
+        return id === '2';
+      });
+      expect(result).toBe(true);
+      result = conditionTreeEvaluator.evaluate(['not', '1', '2', '3'], function(id: string) {
+        return id === '1' ? null : id === '3';
+      });
+      expect(result).toBeNull();
+    });
+
+    describe('null handling', function() {
+      it('should return null when operand evaluates to null', function() {
+        expect(
+          conditionTreeEvaluator.evaluate(['not', conditionA], function() {
+            return null;
+          })
+        ).toBeNull();
+      });
+
+      it('should return null when there are no operands', function() {
+        expect(
+          conditionTreeEvaluator.evaluate(['not'], function() {
+            return null;
+          })
+        ).toBeNull();
+      });
+    });
+  });
+
+  describe('implicit operator', function() {
+    it('should behave like an "or" operator when the first item in the array is not a recognized operator', function() {
+      const leafEvaluator = vi.fn();
+      leafEvaluator.mockImplementationOnce(() => true).mockImplementationOnce(() => false);
+      expect(conditionTreeEvaluator.evaluate([conditionA, conditionB], leafEvaluator)).toBe(true);
+      expect(
+        conditionTreeEvaluator.evaluate([conditionA, conditionB], function() {
+          return false;
+        })
+      ).toBe(false);
+    });
+  });
+});