Add unit tests for ParseVersion function

Tests basic version parsing, v prefix stripping, prerelease,
build metadata, and error cases for invalid input.

internal/updates/version_test.go

@@ -53,6 +53,88 @@ func TestNormalizeVersionString(t *testing.T) {
 	}
 }
 
+func TestParseVersion(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name       string
+		input      string
+		wantErr    bool
+		wantMajor  int
+		wantMinor  int
+		wantPatch  int
+		wantPrerel string
+		wantBuild  string
+	}{
+		{
+			name:      "basic version",
+			input:     "4.24.0",
+			wantMajor: 4, wantMinor: 24, wantPatch: 0,
+		},
+		{
+			name:      "with v prefix",
+			input:     "v4.24.0",
+			wantMajor: 4, wantMinor: 24, wantPatch: 0,
+		},
+		{
+			name:       "with prerelease",
+			input:      "4.24.0-rc.3",
+			wantMajor:  4, wantMinor: 24, wantPatch: 0,
+			wantPrerel: "rc.3",
+		},
+		{
+			name:      "with build metadata",
+			input:     "4.24.0+build.123",
+			wantMajor: 4, wantMinor: 24, wantPatch: 0,
+			wantBuild: "build.123",
+		},
+		{
+			name:       "with prerelease and build",
+			input:      "4.24.0-rc.3+build.123",
+			wantMajor:  4, wantMinor: 24, wantPatch: 0,
+			wantPrerel: "rc.3",
+			wantBuild:  "build.123",
+		},
+		{
+			name:    "invalid format",
+			input:   "not-a-version",
+			wantErr: true,
+		},
+		{
+			name:    "empty string",
+			input:   "",
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got, err := ParseVersion(tc.input)
+			if tc.wantErr {
+				if err == nil {
+					t.Fatalf("ParseVersion(%q) expected error, got nil", tc.input)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("ParseVersion(%q) unexpected error: %v", tc.input, err)
+			}
+			if got.Major != tc.wantMajor || got.Minor != tc.wantMinor || got.Patch != tc.wantPatch {
+				t.Fatalf("ParseVersion(%q) = %d.%d.%d, want %d.%d.%d",
+					tc.input, got.Major, got.Minor, got.Patch, tc.wantMajor, tc.wantMinor, tc.wantPatch)
+			}
+			if got.Prerelease != tc.wantPrerel {
+				t.Fatalf("ParseVersion(%q).Prerelease = %q, want %q", tc.input, got.Prerelease, tc.wantPrerel)
+			}
+			if got.Build != tc.wantBuild {
+				t.Fatalf("ParseVersion(%q).Build = %q, want %q", tc.input, got.Build, tc.wantBuild)
+			}
+		})
+	}
+}
+
 func TestDetectChannelFromVersion(t *testing.T) {
 	t.Parallel()