tiny.game.golden

1//! An exact byte comparison between a saved reference output and a new one. A test wants to know2//! whether a run produced the same output as its saved reference, and the first offset at which the3//! two differ. Parsing both outputs to find a meaningful difference takes work that only a run4//! whose bytes differ needs. `compare` walks both outputs byte by byte and returns whether they5//! match, the offset of the first difference and both lengths (`Comparison`). When one output6//! matches the start of the other, the first difference is at the shorter output's length. A caller7//! runs the byte comparison first and parses both outputs only when they differ.8const std = @import("std");910/// The result of comparing a new output with its reference: whether they match, the first offset at11/// which they differ, and both lengths. A test reads `equal` to decide whether it has to look12/// closer at the two outputs.13pub const Comparison = struct {14    /// True when both outputs have the same length and the same bytes.15    equal: bool,16    /// The offset of the first byte at which the outputs differ, or `null` when they match. When17    /// one output matches the start of the other, the offset is the shorter output's length.18    first_difference: ?usize,19    /// The length of the reference output in bytes.20    expected_bytes: usize,21    /// The length of the new output in bytes.22    actual_bytes: usize,23};2425/// Compares a new output, `actual`, with its reference, `expected`, byte by byte. A test calls it26/// on its saved reference and the output of a fresh run. The call stops at the first differing27/// byte. The call allocates nothing.28pub fn compare(expected: []const u8, actual: []const u8) Comparison {29    const extent = @min(expected.len, actual.len);30    for (expected[0..extent], actual[0..extent], 0..) |a, b, i| {31        if (a != b) return .{ .equal = false, .first_difference = i, .expected_bytes = expected.len, .actual_bytes = actual.len };32    }33    return .{34        .equal = expected.len == actual.len,35        .first_difference = if (expected.len == actual.len) null else extent,36        .expected_bytes = expected.len,37        .actual_bytes = actual.len,38    };39}4041test "goldens compare exact output bytes" {42    try std.testing.expect(compare("abc", "abc").equal);43    try std.testing.expectEqual(@as(?usize, 2), compare("abc", "abd").first_difference);44    try std.testing.expectEqual(@as(?usize, 3), compare("abc", "abcd").first_difference);45}

1pub const golden = @import("golden.zig");