diff --git a/.gitignore b/.gitignore
index 4b65671..b030237 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,8 +18,5 @@
 coverage.out
 *.test
 
-# Stray/unwanted test file from previous work
-config/config_test.go
-
 # Large session-generated review notes
 docs/
\ No newline at end of file
diff --git a/config/config_test.go b/config/config_test.go
new file mode 100644
index 0000000..b931086
--- /dev/null
+++ b/config/config_test.go
@@ -0,0 +1,68 @@
+package config
+
+import (
+	"testing"
+)
+
+func TestConfig_Validate(t *testing.T) {
+	tests := []struct {
+		name    string
+		cfg     Config
+		wantErr bool
+	}{
+		{
+			name: "valid defaults",
+			cfg:  GetDefaultConfig(),
+		},
+		{
+			name: "negative concurrency",
+			cfg: Config{
+				MaxConcurrentRequests: -1,
+			},
+			wantErr: true,
+		},
+		{
+			name: "invalid memory gc algorithm",
+			cfg: Config{
+				Cache: CacheConfig{
+					Memory: MemoryConfig{
+						Size:        "1GB",
+						GCAlgorithm: "invalid",
+					},
+				},
+			},
+			wantErr: true,
+		},
+		{
+			name: "disk enabled without path",
+			cfg: Config{
+				Cache: CacheConfig{
+					Disk: DiskConfig{
+						Size:        "100GB",
+						GCAlgorithm: "lru",
+					},
+				},
+			},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.cfg.Validate()
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Validate() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestGetDefaultConfig(t *testing.T) {
+	def := GetDefaultConfig()
+	if def.ListenAddress != ":80" {
+		t.Error("expected default listen address :80")
+	}
+	if def.Cache.Memory.Size != "1GB" {
+		t.Error("expected default memory 1GB")
+	}
+}