[DK TestAI] Add unit tests for requestHandlerLabel

src/service/metrics/requestHandlerLabel.test.ts

@@ -0,0 +1,279 @@
+import { UNNAMED_REQUEST_HANDLER, requestHandlerLabel } from './requestHandlerLabel'
+
+describe('requestHandlerLabel', () => {
+  describe('UNNAMED_REQUEST_HANDLER constant', () => {
+    it('should export the constant with value "undefined"', () => {
+      // Arrange & Act & Assert
+      expect(UNNAMED_REQUEST_HANDLER).toBe('undefined')
+    })
+
+    it('should be a non-empty string', () => {
+      // Arrange & Act & Assert
+      expect(typeof UNNAMED_REQUEST_HANDLER).toBe('string')
+      expect(UNNAMED_REQUEST_HANDLER.length).toBeGreaterThan(0)
+    })
+  })
+
+  describe('requestHandlerLabel function', () => {
+    describe('happy path', () => {
+      it('should return the provided requestHandlerName when it is a non-empty string', () => {
+        // Arrange
+        const handlerName = 'getUserById'
+
+        // Act
+        const result = requestHandlerLabel(handlerName)
+
+        // Assert
+        expect(result).toBe('getUserById')
+      })
+
+      it('should return the provided requestHandlerName for various valid handler names', () => {
+        // Arrange
+        const testCases = [
+          'listUsers',
+          'createPost',
+          'deleteComment',
+          'updateProfile',
+          'builtin:notFound',
+          'builtin:error',
+          'middleware:auth'
+        ]
+
+        // Act & Assert
+        testCases.forEach(handlerName => {
+          expect(requestHandlerLabel(handlerName)).toBe(handlerName)
+        })
+      })
+
+      it('should handle handler names with special characters', () => {
+        // Arrange
+        const specialNames = [
+          'handler-with-dash',
+          'handler_with_underscore',
+          'handler.with.dot',
+          'handler/with/slash',
+          'handler:with:colon'
+        ]
+
+        // Act & Assert
+        specialNames.forEach(name => {
+          expect(requestHandlerLabel(name)).toBe(name)
+        })
+      })
+
+      it('should handle handler names with numbers', () => {
+        // Arrange
+        const nameWithNumbers = 'handler123'
+
+        // Act
+        const result = requestHandlerLabel(nameWithNumbers)
+
+        // Assert
+        expect(result).toBe('handler123')
+      })
+    })
+
+    describe('edge cases - undefined and null', () => {
+      it('should return UNNAMED_REQUEST_HANDLER when requestHandlerName is undefined', () => {
+        // Arrange
+        const handlerName = undefined
+
+        // Act
+        const result = requestHandlerLabel(handlerName)
+
+        // Assert
+        expect(result).toBe(UNNAMED_REQUEST_HANDLER)
+        expect(result).toBe('undefined')
+      })
+
+      it('should return UNNAMED_REQUEST_HANDLER when no argument is provided', () => {
+        // Arrange & Act
+        const result = requestHandlerLabel()
+
+        // Assert
+        expect(result).toBe(UNNAMED_REQUEST_HANDLER)
+        expect(result).toBe('undefined')
+      })
+    })
+
+    describe('edge cases - empty strings', () => {
+      it('should return UNNAMED_REQUEST_HANDLER when requestHandlerName is an empty string', () => {
+        // Arrange
+        const handlerName = ''
+
+        // Act
+        const result = requestHandlerLabel(handlerName)
+
+        // Assert
+        expect(result).toBe(UNNAMED_REQUEST_HANDLER)
+        expect(result).toBe('undefined')
+      })
+
+      it('should fall back for empty string to ensure label is never emitted empty', () => {
+        // Arrange
+        const emptyHandler = ''
+
+        // Act
+        const result = requestHandlerLabel(emptyHandler)
+
+        // Assert
+        expect(result).not.toBe('')
+        expect(result.length).toBeGreaterThan(0)
+      })
+    })
+
+    describe('edge cases - whitespace-only strings', () => {
+      it('should NOT fall back for whitespace-only strings (they are truthy)', () => {
+        // Arrange
+        const whitespaceHandler = '   '
+
+        // Act
+        const result = requestHandlerLabel(whitespaceHandler)
+
+        // Assert
+        expect(result).toBe('   ')
+      })
+
+      it('should preserve single space string', () => {
+        // Arrange
+        const singleSpace = ' '
+
+        // Act
+        const result = requestHandlerLabel(singleSpace)
+
+        // Assert
+        expect(result).toBe(' ')
+      })
+    })
+
+    describe('consistency with aggregation expectations', () => {
+      it('should return consistent string for undefined across multiple calls', () => {
+        // Arrange & Act
+        const result1 = requestHandlerLabel(undefined)
+        const result2 = requestHandlerLabel()
+        const result3 = requestHandlerLabel('')
+
+        // Assert
+        expect(result1).toBe(result2)
+        expect(result2).toBe(result3)
+        expect(result1).toBe('undefined')
+      })
+
+      it('should ensure label is never empty string in any scenario', () => {
+        // Arrange
+        const scenarios = [
+          undefined,
+          '',
+          'validHandler'
+        ]
+
+        // Act & Assert
+        scenarios.forEach(scenario => {
+          const result = requestHandlerLabel(scenario)
+          expect(result).not.toBe('')
+          expect(result.length).toBeGreaterThan(0)
+        })
+      })
+
+      it('should preserve historical series identity with "undefined" string', () => {
+        // Arrange
+        const undefinedHandler = undefined
+
+        // Act
+        const result = requestHandlerLabel(undefinedHandler)
+
+        // Assert
+        expect(result).toBe('undefined')
+        // Verify it matches the constant to ensure prom-client serialization consistency
+        expect(result).toBe(UNNAMED_REQUEST_HANDLER)
+      })
+    })
+
+    describe('type safety', () => {
+      it('should return a string in all cases', () => {
+        // Arrange
+        const testInputs = [undefined, '', 'handler', 'builtin:notFound']
+
+        // Act & Assert
+        testInputs.forEach(input => {
+          const result = requestHandlerLabel(input)
+          expect(typeof result).toBe('string')
+        })
+      })
+
+      it('should always return UNNAMED_REQUEST_HANDLER or the provided string', () => {
+        // Arrange
+        const validHandler = 'myHandler'
+        const unnamedHandler = undefined
+
+        // Act
+        const resultValid = requestHandlerLabel(validHandler)
+        const resultUnnamed = requestHandlerLabel(unnamedHandler)
+
+        // Assert
+        expect(resultValid === validHandler || resultValid === UNNAMED_REQUEST_HANDLER).toBe(true)
+        expect(resultUnnamed === UNNAMED_REQUEST_HANDLER).toBe(true)
+      })
+    })
+
+    describe('long handler names', () => {
+      it('should handle very long handler names', () => {
+        // Arrange
+        const longName = 'a'.repeat(1000)
+
+        // Act
+        const result = requestHandlerLabel(longName)
+
+        // Assert
+        expect(result).toBe(longName)
+        expect(result.length).toBe(1000)
+      })
+    })
+
+    describe('numeric and special string inputs', () => {
+      it('should handle numeric strings', () => {
+        // Arrange
+        const numericString = '12345'
+
+        // Act
+        const result = requestHandlerLabel(numericString)
+
+        // Assert
+        expect(result).toBe('12345')
+      })
+
+      it('should handle zero as a string', () => {
+        // Arrange
+        const zeroString = '0'
+
+        // Act
+        const result = requestHandlerLabel(zeroString)
+
+        // Assert
+        expect(result).toBe('0')
+      })
+
+      it('should handle the string "false"', () => {
+        // Arrange
+        const falseString = 'false'
+
+        // Act
+        const result = requestHandlerLabel(falseString)
+
+        // Assert
+        expect(result).toBe('false')
+      })
+
+      it('should handle the string "null"', () => {
+        // Arrange
+        const nullString = 'null'
+
+        // Act
+        const result = requestHandlerLabel(nullString)
+
+        // Assert
+        expect(result).toBe('null')
+      })
+    })
+  })
+})