Add tests for lazy regexp initialization

Signed-off-by: Kimmo Lehto <klehto@mirantis.com>

lazy_test.go

@@ -0,0 +1,83 @@
+package validator
+
+import (
+	"regexp"
+	"sync"
+	"testing"
+)
+
+// TestLazyRegexCompile_Basic tests that lazyRegexCompile compiles the regex only once and caches the result.
+func TestLazyRegexCompile_Basic(t *testing.T) {
+	alphaRegexString := "^[a-zA-Z]+$"
+	alphaRegex := lazyRegexCompile(alphaRegexString)
+
+	callCount := 0
+	originalFunc := alphaRegex
+	alphaRegex = func() *regexp.Regexp {
+		callCount++
+		return originalFunc()
+	}
+
+	// Call the function multiple times
+	for i := 0; i < 10; i++ {
+		result := alphaRegex()
+		if result == nil {
+			t.Fatalf("Expected non-nil result")
+		}
+		if !result.MatchString("test") {
+			t.Fatalf("Expected regex to match 'test'")
+		}
+	}
+
+	if callCount != 10 {
+		t.Fatalf("Expected call count to be 10, got %d", callCount)
+	}
+}
+
+// TestLazyRegexCompile_Concurrent tests that lazyRegexCompile works correctly when called concurrently.
+func TestLazyRegexCompile_Concurrent(t *testing.T) {
+	alphaRegexString := "^[a-zA-Z]+$"
+	alphaRegex := lazyRegexCompile(alphaRegexString)
+
+	var wg sync.WaitGroup
+	const numGoroutines = 100
+
+	// Use a map to ensure all results point to the same instance
+	results := make(map[*regexp.Regexp]bool)
+	var mu sync.Mutex
+
+	// Call the function concurrently
+	for i := 0; i < numGoroutines; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			result := alphaRegex()
+			if result == nil {
+				t.Errorf("Expected non-nil result")
+			}
+			mu.Lock()
+			results[result] = true
+			mu.Unlock()
+		}()
+	}
+	wg.Wait()
+
+	if len(results) != 1 {
+		t.Fatalf("Expected one unique regex instance, got %d", len(results))
+	}
+}
+
+// TestLazyRegexCompile_Panic tests that if the regex compilation panics, the panic value is propagated consistently.
+func TestLazyRegexCompile_Panic(t *testing.T) {
+	faultyRegexString := "[a-z"
+	alphaRegex := lazyRegexCompile(faultyRegexString)
+
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fatalf("Expected a panic, but none occurred")
+		}
+	}()
+
+	// Call the function, which should panic
+	alphaRegex()
+}