From 8f6cefcd68540f984ae916a456d19c37f464635d Mon Sep 17 00:00:00 2001
From: Natercio Moniz <natercio.moniz@gmail.com>
Date: Sat, 1 Aug 2026 16:31:30 +0100
Subject: [PATCH] stronger kind tests and validation

---
 internal/kind.go      |  16 ++++--
 internal/kind_test.go | 125 +++++++++++++++++++++++++++---------------
 internal/report.go    |   2 +
 3 files changed, 93 insertions(+), 50 deletions(-)

diff --git a/internal/kind.go b/internal/kind.go
index 50c8af0..9eee9a4 100644
--- a/internal/kind.go
+++ b/internal/kind.go
@@ -7,11 +7,12 @@ const (
 	KindBuy
 	KindSell
 	KindSplit
+	sentinelKind
 )
 
-// String returns a human readable value
-func (d Kind) String() string {
-	switch d {
+// String returns a unique string value for Kind k
+func (k Kind) String() string {
+	switch k {
 	case KindBuy:
 		return "buy"
 	case KindSell:
@@ -23,8 +24,13 @@ func (d Kind) String() string {
 	}
 }
 
-// Is returns true when k equals o
+// Valid returns true if k is an accepted value for the Kind type
+func (k Kind) Valid() bool {
+	return k > 0 && k < sentinelKind
+}
+
+// Is returns true when k and o are valid and equal.
 func (k Kind) Is(o any) bool {
 	other, ok := o.(Kind)
-	return ok && k == other
+	return ok && k.Valid() && k == other
 }
diff --git a/internal/kind_test.go b/internal/kind_test.go
index a52d7e6..c5af02b 100644
--- a/internal/kind_test.go
+++ b/internal/kind_test.go
@@ -1,60 +1,95 @@
 package internal
 
-import "testing"
+import (
+	"fmt"
+	"testing"
+)
 
 func TestSide_String(t *testing.T) {
-	tests := []struct {
-		name string
-		side Kind
-		want string
-	}{
-		{"buy", KindBuy, "buy"},
-		{"sell", KindSell, "sell"},
-		{"unknown", KindUnknown, "unknown"},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := tt.side.String(); got != tt.want {
-				t.Errorf("want Side.String() to be %v but got %v", tt.want, got)
+	const unknown = "unknown"
+
+	seen := make(map[string]Kind, sentinelKind)
+	for k := Kind(1); k < sentinelKind; k++ {
+		t.Run(fmt.Sprintf("Kind %d", k), func(t *testing.T) {
+			str := k.String()
+
+			if other, ok := seen[str]; ok {
+				t.Errorf("want Kind(%d).String to be unique but was a duplicate of Kind(%d)", k, other)
+			} else {
+				seen[str] = k
+			}
+
+			if len(str) == 0 {
+				t.Errorf("want Kind(%d).String to be non-empty", k)
+			}
+
+			if str == unknown {
+				t.Errorf("want Kind(%d).String to be a known value", k)
 			}
 		})
 	}
+
+	if KindUnknown.String() != unknown {
+		t.Errorf("want Kind(0) to be unknown")
+	}
+
+	if Kind(sentinelKind).String() != unknown {
+		t.Errorf("want Kind(%d) to be unknown", sentinelKind)
+	}
 }
 
-func TestSide_IsBuy(t *testing.T) {
-	tests := []struct {
-		name string
-		side Kind
-		want bool
-	}{
-		{"buy", KindBuy, true},
-		{"sell", KindSell, false},
-		{"unknown", KindUnknown, false},
+func TestSide_Valid(t *testing.T) {
+	for k := Kind(1); k < sentinelKind; k++ {
+		if !k.Valid() {
+			t.Errorf("want %s(%d) to be valid", k, k)
+		}
 	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := tt.side.Is(KindBuy); got != tt.want {
-				t.Errorf("want Side.IsBuy() to be %v but got %v", tt.want, got)
-			}
-		})
+
+	if KindUnknown.Valid() {
+		t.Errorf("want Kind(0) to be invalid")
+	}
+
+	if Kind(sentinelKind).Valid() {
+		t.Errorf("want Kind(%d) to be invalid", sentinelKind)
 	}
 }
 
-func TestSide_IsSell(t *testing.T) {
-	tests := []struct {
-		name string
-		side Kind
-		want bool
-	}{
-		{"buy", KindBuy, false},
-		{"sell", KindSell, true},
-		{"unknown", KindUnknown, false},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := tt.side.Is(KindSell); got != tt.want {
-				t.Errorf("want Side.IsSell() to be %v but got %v", tt.want, got)
+func TestSide_Is(t *testing.T) {
+	t.Run("valid is self", func(t *testing.T) {
+		for k := Kind(1); k < sentinelKind; k++ {
+			if !k.Is(k) {
+				t.Errorf("want Kind(%d).Is(%d) to be true", k, k)
 			}
-		})
-	}
+		}
+	})
+
+	t.Run("valid is unknown", func(t *testing.T) {
+		for k := Kind(1); k < sentinelKind; k++ {
+			if k.Is(KindUnknown) {
+				t.Errorf("want Kind(%d).Is(0) to be false", k)
+			}
+
+			if k.Is(sentinelKind) {
+				t.Errorf("want Kind(%d).Is(%d) to be false", k, sentinelKind)
+			}
+
+			if k.Is(struct{}{}) {
+				t.Errorf("want Kind(%d).Is(other type) to be false", k)
+			}
+		}
+	})
+
+	t.Run("unknown is unknown", func(t *testing.T) {
+		if KindUnknown.Is(KindUnknown) {
+			t.Errorf("want Kind(0).Is(0) to be false")
+		}
+
+		if KindUnknown.Is(sentinelKind) {
+			t.Errorf("want Kind(0).Is(%d) to be false", sentinelKind)
+		}
+
+		if sentinelKind.Is(sentinelKind) {
+			t.Errorf("want Kind(%d).Is(%d) to be false", sentinelKind, sentinelKind)
+		}
+	})
 }
diff --git a/internal/report.go b/internal/report.go
index eb0e6b0..4368653 100644
--- a/internal/report.go
+++ b/internal/report.go
@@ -132,6 +132,8 @@ func BuildReport(ctx context.Context, reader RecordReader, writer ReportWriter,
 				buysCount++
 			} else if rec.Kind().Is(KindSell) {
 				sellsCount++
+			} else if !rec.Kind().Valid() {
+				return fmt.Errorf("cannot process Kind(%d)", rec.Kind())
 			}
 
 			lastTimestamp = rec.Timestamp()