Assertions & messages

The load-bearing job of this layer is the exact failure message. Each assert_*/refute_* returns nil on pass or an *Assertion/*Skip whose message is byte-identical to the minitest 5.x gem’s. Every message below is verified against the live gem by the differential oracle.

The message model

Minitest::Assertions#message composes an optional custom message with a default and an ending:

a custom message is chomped of one trailing . then rendered as "#{msg}.\n";
the default follows;
the ending is . for most assertions, and empty for assert_equal’s diff form (so the diff gets no trailing dot).

a.AssertEqual(rInt(1), rInt(2), "oops")
// oops.
// Expected: 1
//   Actual: 2

Wording reference

Assertion	Failure message (default)
`assert`	`Expected <mu_pp> to be truthy.`
`refute`	`Expected <mu_pp> to not be truthy.`
`assert_equal`	`Expected: <exp>`⏎ `Actual: <act>` (diff form, no trailing dot)
`refute_equal`	`Expected <act> to not be equal to <exp>.`
`assert_nil`	`Expected <mu_pp> to be nil.`
`assert_empty`	`Expected <mu_pp> to be empty.` (first asserts `respond_to? :empty?`)
`assert_includes`	`Expected <coll> to include <obj>.`
`assert_instance_of`	`Expected <obj> to be an instance of <cls>, not <class>.`
`assert_kind_of`	`Expected <obj> to be a kind of <cls>, not <class>.`
`assert_respond_to`	`Expected <obj> (<class>) to respond to #<meth>.`
`assert_match`	`Expected <regexp> to match <obj>.` (a String matcher is promoted)
`assert_same`	`Expected <act> (oid=N) to be the same as <exp> (oid=N).`
`assert_in_delta`	`Expected \|<exp> - <act>\| (<n>) to be <= <delta>.`
`assert_operator`	`Expected <o1> to be <op> <o2>.`
`assert_predicate`	`Expected <o1> to be <op>.`
`flunk`	`Epic Fail!`
`skip`	`Skipped, no message given`

<mu_pp>, <exp>, <act>, … are the mu_pp inspection of the value. Each refute_* inverts the sense (to not be …).

mu_pp

mu_pp(obj) is obj.inspect, with two 5.x refinements the library reproduces:

a String whose encoding differs from Encoding.default_external, or which is invalidly encoded, gets an encoding annotation;
mu_pp_for_diff additionally normalizes for the diff path.

a.MuPP(rInt(5))            // 5
a.MuPP(rStr("hi"))         // "hi"
a.MuPP(rArr{rInt(1), rInt(2)}) // [1, 2]
a.MuPP(rNil)               // nil
a.MuPP(rSym("foo"))        // :foo

The inspect, ==, =~, include?, respond_to?, class name and __send__ that these messages interpolate all come from the host’s Runtime — the library formats, the host supplies the value semantics.

Float formatting

assert_in_delta / assert_in_epsilon interpolate floats the way Ruby’s Float#to_s does: shortest round-tripping decimal, positional unless the decimal exponent is < -4 or >= 15 (then d.dddde±NN with a signed, ≥2-digit exponent), with Infinity/-Infinity/NaN/-0.0 special-cased. The library reshapes Go’s shortest strconv output to those exact thresholds.

Usage & API Run lifecycle & results