test: add more service layer tests

Coverage: Service 71.7% → 71.8%

- classified_error_test.go (10 tests): error wrapping, Unwrap, errors.Is
- stats_test.go (12 tests): user stats, dashboard stats, daysAgo utility

internal/service/classified_error_test.go

@@ -3,97 +3,72 @@ package service
 import (
 	"errors"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 // =============================================================================
-// Classified Error Tests
+// ClassifiedError Tests
 // =============================================================================
 
-func TestClassifiedError(t *testing.T) {
-	// Test error with message
-	e1 := &classifiedError{message: "custom message", cause: errors.New("cause")}
-	if e1.Error() != "custom message" {
-		t.Errorf("Error() = %q, want %q", e1.Error(), "custom message")
-	}
-
-	// Test error with cause but no message
-	e2 := &classifiedError{cause: errors.New("underlying error")}
-	if e2.Error() != "underlying error" {
-		t.Errorf("Error() = %q, want %q", e2.Error(), "underlying error")
-	}
-
-	// Test error with neither message nor cause
-	e3 := &classifiedError{}
-	if e3.Error() != "" {
-		t.Errorf("Error() = %q, want empty string", e3.Error())
-	}
+func TestClassifiedError_Error_WithMessage(t *testing.T) {
+	err := newValidationError("custom validation message")
+	assert.EqualError(t, err, "custom validation message")
 }
 
-func TestClassifiedErrorUnwrap(t *testing.T) {
-	innerErr := errors.New("inner error")
-	e := &classifiedError{message: "outer", cause: innerErr}
-
-	unwrapped := e.Unwrap()
-	if unwrapped != innerErr {
-		t.Errorf("Unwrap() = %v, want %v", unwrapped, innerErr)
-	}
-
-	// Test errors.Is
-	if !errors.Is(e, innerErr) {
-		t.Error("errors.Is(e, innerErr) = false, want true")
-	}
+func TestClassifiedError_Error_WithEmptyMessage(t *testing.T) {
+	// Create error with only cause
+	err := &classifiedError{cause: ErrValidationFailed}
+	assert.EqualError(t, err, "validation failed")
 }
 
-func TestNewRateLimitError(t *testing.T) {
+func TestClassifiedError_Error_WithNoMessageOrCause(t *testing.T) {
+	// Create error with neither message nor cause
+	err := &classifiedError{}
+	assert.Equal(t, "", err.Error())
+}
+
+func TestClassifiedError_Unwrap(t *testing.T) {
 	err := newRateLimitError("too many requests")
-
-	// Should be a classifiedError
-	var ce *classifiedError
-	if !errors.As(err, &ce) {
-		t.Errorf("errors.As(err, &classifiedError{}) = false")
-	}
-
-	// Should wrap ErrRateLimitExceeded
-	if !errors.Is(err, ErrRateLimitExceeded) {
-		t.Error("errors.Is(err, ErrRateLimitExceeded) = false")
-	}
-
-	// Error message should be "too many requests"
-	if err.Error() != "too many requests" {
-		t.Errorf("err.Error() = %q, want %q", err.Error(), "too many requests")
-	}
-}
-
-func TestNewValidationError(t *testing.T) {
-	err := newValidationError("invalid input")
-
-	// Should be a classifiedError
-	var ce *classifiedError
-	if !errors.As(err, &ce) {
-		t.Errorf("errors.As(err, &classifiedError{}) = false")
-	}
-
-	// Should wrap ErrValidationFailed
-	if !errors.Is(err, ErrValidationFailed) {
-		t.Error("errors.Is(err, ErrValidationFailed) = false")
-	}
-
-	// Error message should be "invalid input"
-	if err.Error() != "invalid input" {
-		t.Errorf("err.Error() = %q, want %q", err.Error(), "invalid input")
-	}
+	
+	// Unwrap should return the cause
+	unwrapped := errors.Unwrap(err)
+	assert.Equal(t, ErrRateLimitExceeded, unwrapped)
 }
 
 func TestErrRateLimitExceeded(t *testing.T) {
-	// ErrRateLimitExceeded is a sentinel error
-	if ErrRateLimitExceeded.Error() != "rate limit exceeded" {
-		t.Errorf("ErrRateLimitExceeded.Error() = %q, want %q", ErrRateLimitExceeded.Error(), "rate limit exceeded")
-	}
+	assert.EqualError(t, ErrRateLimitExceeded, "rate limit exceeded")
 }
 
 func TestErrValidationFailed(t *testing.T) {
-	// ErrValidationFailed is a sentinel error
-	if ErrValidationFailed.Error() != "validation failed" {
-		t.Errorf("ErrValidationFailed.Error() = %q, want %q", ErrValidationFailed.Error(), "validation failed")
-	}
+	assert.EqualError(t, ErrValidationFailed, "validation failed")
+}
+
+func TestErrors_Is_RateLimit(t *testing.T) {
+	// Test that wrapped errors can be identified using errors.Is
+	err := newRateLimitError("too many requests")
+	
+	assert.True(t, errors.Is(err, ErrRateLimitExceeded))
+	assert.False(t, errors.Is(err, ErrValidationFailed))
+}
+
+func TestErrors_Is_Validation(t *testing.T) {
+	err := newValidationError("invalid input")
+	
+	assert.True(t, errors.Is(err, ErrValidationFailed))
+	assert.False(t, errors.Is(err, ErrRateLimitExceeded))
+}
+
+func TestNewRateLimitError(t *testing.T) {
+	err := newRateLimitError("rate limited")
+	
+	assert.EqualError(t, err, "rate limited")
+	assert.True(t, errors.Is(err, ErrRateLimitExceeded))
+}
+
+func TestNewValidationError(t *testing.T) {
+	err := newValidationError("validation failed")
+	
+	assert.EqualError(t, err, "validation failed")
+	assert.True(t, errors.Is(err, ErrValidationFailed))
 }