diff --git a/tests/core/normal.odin b/tests/core/normal.odin
index 065090be3..1f34e3292 100644
--- a/tests/core/normal.odin
+++ b/tests/core/normal.odin
@@ -38,6 +38,7 @@ download_assets :: proc() {
 @(require) import "strings"
 @(require) import "text/i18n"
 @(require) import "text/match"
+@(require) import "text/regex"
 @(require) import "thread"
 @(require) import "time"
 @(require) import "unicode"
diff --git a/tests/core/text/regex/test_core_text_regex.odin b/tests/core/text/regex/test_core_text_regex.odin
new file mode 100644
index 000000000..da44e6b2d
--- /dev/null
+++ b/tests/core/text/regex/test_core_text_regex.odin
@@ -0,0 +1,1012 @@
+package test_core_text_regex
+
+import "core:fmt"
+import "core:io"
+import "core:log"
+import "core:strings"
+import "core:testing"
+import "core:text/regex"
+import "core:text/regex/common"
+import "core:text/regex/parser"
+import "core:text/regex/tokenizer"
+
+
+check_expression_with_flags :: proc(t: ^testing.T, pattern: string, flags: regex.Flags, haystack: string, needles: ..string, loc := #caller_location) {
+	rex, parse_err := regex.create(pattern, flags)
+	if !testing.expect_value(t, parse_err, nil, loc = loc) {
+		log.infof("Failed test's flags were: %v", flags, location = loc)
+		return
+	}
+	defer regex.destroy(rex)
+
+	capture, success := regex.match(rex, haystack)
+	defer {
+		delete(capture.groups)
+		delete(capture.pos)
+	}
+
+	if len(needles) > 0 {
+		testing.expect(t, success, "match failed", loc = loc)
+	}
+
+	matches_aligned := testing.expectf(t, len(needles) == len(capture.groups),
+		"expected %i match groups, got %i (flags: %w)",
+		len(needles), len(capture.groups), flags, loc = loc)
+
+	if matches_aligned {
+		for needle, i in needles {
+			if !testing.expectf(t, capture.groups[i] == needle,
+				"match group %i was %q, expected %q (flags: %w)",
+				i, capture.groups[i], needle, flags, loc = loc) {
+			}
+		}
+	} else {
+		log.infof("match groups were: %v", capture.groups, location = loc)
+	}
+}
+
+check_expression :: proc(t: ^testing.T, pattern, haystack: string, needles: ..string, extra_flags: regex.Flags = {}, loc := #caller_location) {
+	check_expression_with_flags(t, pattern, { .Global } + extra_flags,
+		haystack, ..needles, loc = loc)
+	check_expression_with_flags(t, pattern, { .Global, .No_Optimization } + extra_flags,
+		haystack, ..needles, loc = loc)
+	check_expression_with_flags(t, pattern, { .Global, .Unicode } + extra_flags,
+		haystack, ..needles, loc = loc)
+	check_expression_with_flags(t, pattern, { .Global, .Unicode, .No_Optimization } + extra_flags,
+		haystack, ..needles, loc = loc)
+}
+
+
+@test
+test_concatenation :: proc(t: ^testing.T) {
+	check_expression(t, "abc", "abc", "abc")
+}
+
+@test
+test_rune_class :: proc(t: ^testing.T) {
+	EXPR :: "[abc]"
+	check_expression(t, EXPR, "a", "a")
+	check_expression(t, EXPR, "b", "b")
+	check_expression(t, EXPR, "c", "c")
+}
+
+@test
+test_rune_ranges :: proc(t: ^testing.T) {
+	EXPR :: "0x[0-9A-Fa-f]+"
+	check_expression(t, EXPR, "0x0065c816", "0x0065c816")
+}
+
+@test
+test_rune_range_terminal_dash :: proc(t: ^testing.T) {
+	{
+		EXPR :: "[a-]"
+		check_expression(t, EXPR, "a", "a")
+		check_expression(t, EXPR, "-", "-")
+	}
+	{
+		EXPR :: "[-a]"
+		check_expression(t, EXPR, "a", "a")
+		check_expression(t, EXPR, "-", "-")
+	}
+	{
+		EXPR :: "[-a-]"
+		check_expression(t, EXPR, "a", "a")
+		check_expression(t, EXPR, "-", "-")
+	}
+	{
+		EXPR :: "[-]"
+		check_expression(t, EXPR, "-", "-")
+	}
+	{
+		EXPR :: "[--]"
+		check_expression(t, EXPR, "-", "-")
+	}
+	{
+		EXPR :: "[---]"
+		check_expression(t, EXPR, "-", "-")
+	}
+}
+
+@test
+test_rune_range_escaping_class :: proc(t: ^testing.T) {
+	EXPR :: `[\]a\[\.]`
+	check_expression(t, EXPR, "a", "a")
+	check_expression(t, EXPR, "[", "[")
+	check_expression(t, EXPR, "]", "]")
+	check_expression(t, EXPR, ".", ".")
+	check_expression(t, EXPR, "b")
+}
+
+@test
+test_negated_rune_class :: proc(t: ^testing.T) {
+	EXPR :: "[^ac-d]"
+	check_expression(t, EXPR, "a")
+	check_expression(t, EXPR, "b", "b")
+	check_expression(t, EXPR, "e", "e")
+	check_expression(t, EXPR, "c")
+	check_expression(t, EXPR, "d")
+}
+
+@test
+test_shorthand_classes :: proc(t: ^testing.T) {
+	EXPR_P :: `\d\w\s`
+	check_expression(t, EXPR_P, "1a ", "1a ")
+	check_expression(t, EXPR_P, "a!1")
+	EXPR_N :: `\D\W\S`
+	check_expression(t, EXPR_N, "a!1", "a!1")
+	check_expression(t, EXPR_N, "1a ")
+}
+
+@test
+test_shorthand_classes_in_classes :: proc(t: ^testing.T) {
+	EXPR_P :: `[\d][\w][\s]`
+	check_expression(t, EXPR_P, "1a ", "1a ")
+	check_expression(t, EXPR_P, "a!1")
+	EXPR_NP :: `[^\d][^\w][^\s]`
+	check_expression(t, EXPR_NP, "a!1", "a!1")
+	check_expression(t, EXPR_NP, "1a ")
+	EXPR_N :: `[\D][\W][\S]`
+	check_expression(t, EXPR_N, "a!1", "a!1")
+	check_expression(t, EXPR_N, "1a ")
+	EXPR_NN :: `[^\D][^\W][^\S]`
+	check_expression(t, EXPR_NN, "1a ", "1a ")
+	check_expression(t, EXPR_NN, "a!1")
+}
+
+@test
+test_mixed_shorthand_class :: proc(t: ^testing.T) {
+	EXPR_P :: `[\d\s]+`
+	check_expression(t, EXPR_P, "0123456789 98", "0123456789 98")
+	check_expression(t, EXPR_P, "!@#$%^&*()_()")
+	EXPR_NP :: `[^\d\s]+`
+	check_expression(t, EXPR_NP, "!@#$%^&*()_()", "!@#$%^&*()_()")
+	check_expression(t, EXPR_NP, "0123456789 98")
+}
+
+@test
+test_wildcard :: proc(t: ^testing.T) {
+	EXPR :: "."
+	check_expression(t, EXPR, "a", "a")
+	check_expression(t, EXPR, ".", ".")
+}
+
+@test
+test_alternation :: proc(t: ^testing.T) {
+	EXPR :: "aa|bb|cc"
+	check_expression(t, EXPR, "aa", "aa")
+	check_expression(t, EXPR, "bb", "bb")
+	check_expression(t, EXPR, "cc", "cc")
+}
+
+@test
+test_optional :: proc(t: ^testing.T) {
+	EXPR :: "a?a?a?aaa"
+	check_expression(t, EXPR, "aaa", "aaa")
+}
+
+@test
+test_repeat_zero :: proc(t: ^testing.T) {
+	EXPR :: "a*b"
+	check_expression(t, EXPR, "aaab", "aaab")
+}
+
+@test
+test_repeat_one :: proc(t: ^testing.T) {
+	EXPR :: "a+b"
+	check_expression(t, EXPR, "aaab", "aaab")
+}
+
+@test
+test_greedy :: proc(t: ^testing.T) {
+	HTML :: "<html></html>"
+
+	check_expression(t, "<.+>", HTML, HTML)
+	check_expression(t, "<.*>", HTML, HTML)
+
+	check_expression(t, "aaa?", "aaa", "aaa")
+}
+
+@test
+test_non_greedy :: proc(t: ^testing.T) {
+	HTML :: "<html></html>"
+
+	check_expression(t, "<.+?>", HTML, "<html>")
+	check_expression(t, "<.*?>", HTML, "<html>")
+
+	// NOTE: make a comment about optional non-greedy capture groups
+	check_expression(t, "aaa??", "aaa", "aa")
+}
+
+@test
+test_groups :: proc(t: ^testing.T) {
+	check_expression(t, "a(b)",   "ab", /*|*/ "ab",  "b")
+	check_expression(t, "(a)b",   "ab", /*|*/ "ab",  "a")
+	check_expression(t, "(a)(b)", "ab", /*|*/ "ab",  "a",  "b")
+
+	check_expression(t, "(a(b))", "ab", /*|*/ "ab", "ab",  "b")
+	check_expression(t, "((ab))", "ab", /*|*/ "ab", "ab", "ab")
+	check_expression(t, "((a)b)", "ab", /*|*/ "ab", "ab",  "a")
+
+	check_expression(t, "(ab)+",   "ababababab", /*|*/ "ababababab", "ab")
+	check_expression(t, "((ab)+)", "ababababab", /*|*/ "ababababab", "ababababab", "ab")
+}
+
+@test
+test_class_group_repeat :: proc(t: ^testing.T) {
+	EXPR_1 :: "([0-9]:?)+"
+	EXPR_2 :: "([0-9]+:?)+"
+	check_expression(t, EXPR_1, "123:456:789", "123:456:789", "9")
+	check_expression(t, EXPR_2, "123:456:789", "123:456:789", "789")
+}
+
+@test
+test_non_capture_group :: proc(t: ^testing.T) {
+	EXPR :: "(?:a|b)c"
+	check_expression(t, EXPR, "ac", "ac")
+	check_expression(t, EXPR, "bc", "bc")
+	check_expression(t, EXPR, "cc")
+}
+
+@test
+test_optional_capture_group :: proc(t: ^testing.T) {
+	EXPR :: "^(blue|straw)?berry"
+	check_expression(t, EXPR, "berry", "berry")
+	check_expression(t, EXPR, "blueberry", "blueberry", "blue")
+	check_expression(t, EXPR, "strawberry", "strawberry", "straw")
+	check_expression(t, EXPR, "cranberry")
+}
+
+@test
+test_max_capture_groups :: proc(t: ^testing.T) {
+	EXPR :: "(1)(2)(3)(4)(5)(6)(7)(8)(9)"
+	check_expression(t, EXPR, "123456789", "123456789",
+		"1", "2", "3", "4", "5", "6", "7", "8", "9")
+}
+
+@test
+test_repetition :: proc(t: ^testing.T) {
+	{
+		EXPR :: "^a{3}$"
+		check_expression(t, EXPR, "aaa", "aaa")
+		check_expression(t, EXPR, "aaaa")
+	}
+	{
+		EXPR :: "^a{3,5}$"
+		check_expression(t, EXPR, "aaa", "aaa")
+		check_expression(t, EXPR, "aaaa", "aaaa")
+		check_expression(t, EXPR, "aaaaa", "aaaaa")
+		check_expression(t, EXPR, "aaaaaa")
+	}
+	{
+		EXPR :: "^(?:meow){2}$"
+		check_expression(t, EXPR, "meow")
+		check_expression(t, EXPR, "meowmeow", "meowmeow")
+		check_expression(t, EXPR, "meowmeowmeow")
+	}
+	{
+		EXPR :: "a{2,}"
+		check_expression(t, EXPR, "a")
+		check_expression(t, EXPR, "aa", "aa")
+		check_expression(t, EXPR, "aaa", "aaa")
+	}
+	{
+		EXPR :: "a{,2}"
+		check_expression(t, EXPR, "a", "a")
+		check_expression(t, EXPR, "aa", "aa")
+		check_expression(t, EXPR, "aaa", "aa")
+	}
+	{
+		EXPR :: "^a{3,3}$"
+		check_expression(t, EXPR, "aa")
+		check_expression(t, EXPR, "aaa", "aaa")
+		check_expression(t, EXPR, "aaaa")
+	}
+	{
+		EXPR :: "a{0,}"
+		check_expression(t, EXPR, "aaa", "aaa")
+	}
+}
+
+@test
+test_repeated_groups :: proc(t: ^testing.T) {
+	{
+		EXPR :: "(ab){3}"
+		check_expression(t, EXPR, "ababab", "ababab", "ab")
+	}
+	{
+		EXPR :: "((?:ab){3})"
+		check_expression(t, EXPR, "ababab", "ababab", "ababab")
+	}
+}
+
+@test
+test_escaped_newline :: proc(t: ^testing.T) {
+	EXPR :: `\n[\n]`
+	check_expression(t, EXPR, "\n\n", "\n\n")
+}
+
+@test
+test_anchors :: proc(t: ^testing.T) {
+	{
+		EXPR :: "^ab"
+		check_expression(t, EXPR, "ab", "ab")
+		check_expression(t, EXPR, "aab")
+	}
+	{
+		EXPR :: "ab$"
+		check_expression(t, EXPR, "ab", "ab")
+		check_expression(t, EXPR, "aab", "ab")
+	}
+	{
+		EXPR :: "^ab$"
+		check_expression(t, EXPR, "ab", "ab")
+		check_expression(t, EXPR, "aab")
+	}
+}
+
+@test
+test_grouped_anchors :: proc(t: ^testing.T) {
+	{
+		EXPR :: "^a|b"
+		check_expression(t, EXPR, "ab", "a")
+		check_expression(t, EXPR, "ba", "b")
+	}
+	{
+		EXPR :: "b|c$"
+		check_expression(t, EXPR, "ac", "c")
+		check_expression(t, EXPR, "cb", "b")
+	}
+	{
+		EXPR :: "^hellope$|world"
+		check_expression(t, EXPR, "hellope", "hellope")
+		check_expression(t, EXPR, "hellope world", "world")
+	}
+}
+
+@test
+test_empty_alternation :: proc(t: ^testing.T) {
+	{
+		EXPR :: "(?:a|)b"
+		check_expression(t, EXPR, "ab", "ab")
+		check_expression(t, EXPR, "b", "b")
+	}
+	{
+		EXPR :: "(?:|a)b"
+		check_expression(t, EXPR, "ab", "ab")
+		check_expression(t, EXPR, "b", "b")
+	}
+	{
+		EXPR :: "|b"
+		check_expression(t, EXPR, "b", "")
+		check_expression(t, EXPR, "", "")
+	}
+	{
+		EXPR :: "a|"
+		check_expression(t, EXPR, "a", "a")
+		check_expression(t, EXPR, "", "")
+	}
+	{
+		EXPR :: "|"
+		check_expression(t, EXPR, "a", "")
+		check_expression(t, EXPR, "", "")
+	}
+}
+
+@test
+test_empty_class :: proc(t: ^testing.T) {
+	EXPR :: "a[]b"
+	check_expression(t, EXPR, "ab", "ab")
+}
+
+@test
+test_dot_in_class :: proc(t: ^testing.T) {
+	EXPR :: `[a\..]`
+	check_expression(t, EXPR, "a", "a")
+	check_expression(t, EXPR, ".", ".")
+	check_expression(t, EXPR, "b")
+}
+
+
+@test
+test_word_boundaries :: proc(t: ^testing.T) {
+	STR :: "This is an island."
+	{
+		EXPR :: `\bis\b`
+		check_expression(t, EXPR, STR, "is")
+	}
+	{
+		EXPR :: `\bis\w+`
+		check_expression(t, EXPR, STR, "island")
+	}
+	{
+		EXPR :: `\w+is\b`
+		check_expression(t, EXPR, STR, "This")
+	}
+	{
+		EXPR :: `\b\w\w\b`
+		check_expression(t, EXPR, STR, "is")
+	}
+}
+
+@test
+test_non_word_boundaries :: proc(t: ^testing.T) {
+	{
+		EXPR :: `.\B.`
+		check_expression(t, EXPR, "ab", "ab")
+		check_expression(t, EXPR, "  ", "  ")
+		check_expression(t, EXPR, "a ")
+		check_expression(t, EXPR, " b")
+	}
+	{
+		EXPR :: `\B.\B`
+		check_expression(t, EXPR, "a")
+		check_expression(t, EXPR, "abc", "b")
+	}
+	{
+		EXPR :: `\B.+`
+		check_expression(t, EXPR, "abc", "bc")
+	}
+	{
+		EXPR :: `.+\B`
+		check_expression(t, EXPR, "abc", "ab")
+	}
+}
+
+@test
+test_empty_patterns :: proc(t: ^testing.T) {
+	{
+		EXPR :: ""
+		check_expression(t, EXPR, "abc", "")
+	}
+	{
+		EXPR :: "^$"
+		check_expression(t, EXPR, "", "")
+		check_expression(t, EXPR, "a")
+	}
+}
+
+@test
+test_unanchored :: proc(t: ^testing.T) {
+	EXPR :: "ab"
+	check_expression(t, EXPR, "cab", "ab")
+}
+
+@test
+test_affixes :: proc(t: ^testing.T) {
+	// This test is for the optimizer.
+	EXPR :: "^(?:samples|ample|sample)$"
+	check_expression(t, EXPR, "sample", "sample")
+	check_expression(t, EXPR, "samples", "samples")
+	check_expression(t, EXPR, "ample", "ample")
+	check_expression(t, EXPR, "amples")
+}
+
+@test
+test_anchored_capture_until_end :: proc(t: ^testing.T) {
+	// This test is for the optimizer.
+	{
+		EXPR :: `^hellope.*$`
+		check_expression(t, EXPR, "hellope world", "hellope world")
+		check_expression(t, EXPR, "hellope", "hellope")
+		check_expression(t, EXPR, "hellope !", "hellope !")
+	}
+	{
+		EXPR :: `^hellope.+$`
+		check_expression(t, EXPR, "hellope world", "hellope world")
+		check_expression(t, EXPR, "hellope")
+		check_expression(t, EXPR, "hellope !", "hellope !")
+	}
+	{
+		EXPR :: `^(aa|bb|cc.+$).*$`
+		check_expression(t, EXPR, "aa", "aa", "aa")
+		check_expression(t, EXPR, "bb", "bb", "bb")
+		check_expression(t, EXPR, "bbaa", "bbaa", "bb")
+		check_expression(t, EXPR, "cc")
+		check_expression(t, EXPR, "ccc", "ccc", "ccc")
+		check_expression(t, EXPR, "cccc", "cccc", "cccc")
+	}
+	// This makes sure that the `.*$` / `.*$` optimization doesn't cause
+	// any issues if someone does something strange like putting it in the
+	// middle of an expression.
+	{
+		EXPR :: `^(a(b.*$)c).*$`
+		check_expression(t, EXPR, "a")
+		check_expression(t, EXPR, "ab")
+		check_expression(t, EXPR, "abc")
+	}
+	{
+		EXPR :: `^(a(b.*$)?c).*$`
+		check_expression(t, EXPR, "a")
+		check_expression(t, EXPR, "ab")
+		check_expression(t, EXPR, "abc")
+		check_expression(t, EXPR, "ac", "ac", "ac")
+		check_expression(t, EXPR, "acc", "acc", "ac")
+	}
+}
+
+@test
+test_unicode_explicitly :: proc(t: ^testing.T) {
+	{
+		EXPR :: "^....!$"
+		check_expression_with_flags(t, EXPR, { .Unicode },
+			"こにちは!", "こにちは!")
+		check_expression_with_flags(t, EXPR, { .Unicode, .No_Optimization },
+			"こにちは!", "こにちは!")
+	}
+	{
+		EXPR :: "こにちは!"
+		check_expression_with_flags(t, EXPR, { .Global, .Unicode },
+			"Hello こにちは!", "こにちは!")
+		check_expression_with_flags(t, EXPR, { .Global, .Unicode, .No_Optimization },
+			"Hello こにちは!", "こにちは!")
+	}
+}
+
+@test
+test_no_capture_match :: proc(t: ^testing.T) {
+	EXPR :: "^abc$"
+
+	rex, parse_err := regex.create(EXPR, { .No_Capture })
+	if !testing.expect_value(t, parse_err, nil) {
+		return
+	}
+	defer regex.destroy(rex)
+
+	_, matched := regex.match(rex, "abc")
+	testing.expect(t, matched)
+}
+
+@test
+test_comments :: proc(t: ^testing.T) {
+	EXPR :: `^[abc]# This is a comment.
+[def]# This is another comment.
+\#$# This is a comment following an escaped '#'.`
+	check_expression(t, EXPR, "ad#", "ad#")
+}
+
+@test
+test_ignore_whitespace :: proc(t: ^testing.T) {
+	EXPR :: "\f" + `
+\ H    e     l   # Note that the first space on this line is escaped, thus it is not ignored.
+	l
+o    p     e [ ]   w   o  rld (?: [ ]) ! # Spaces in classes are fine, too.
+` + "\r"
+
+	check_expression(t, EXPR, " Hellope world !", " Hellope world !", extra_flags = { .Ignore_Whitespace })
+}
+
+@test
+test_case_insensitive :: proc(t: ^testing.T) {
+	EXPR :: `hElLoPe [w!][o-P]+rLd!`
+	check_expression(t, EXPR, "HeLlOpE WoRlD!", "HeLlOpE WoRlD!", extra_flags = { .Case_Insensitive })
+}
+
+@test
+test_multiline :: proc(t: ^testing.T) {
+	{
+		EXPR :: `^hellope$world$`
+		check_expression(t, EXPR, "\nhellope\nworld\n", "\nhellope\nworld\n", extra_flags = { .Multiline })
+		check_expression(t, EXPR, "hellope\nworld", "hellope\nworld", extra_flags = { .Multiline })
+		check_expression(t, EXPR, "hellope\rworld", "hellope\rworld", extra_flags = { .Multiline })
+		check_expression(t, EXPR, "hellope\r\nworld", "hellope\r\nworld", extra_flags = { .Multiline })
+	}
+	{
+		EXPR :: `^?.$`
+		check_expression(t, EXPR, "\nh", "\nh", extra_flags = { .Multiline })
+		check_expression(t, EXPR, "h", "h", extra_flags = { .Multiline })
+	}
+	{
+		EXPR :: `^$`
+		check_expression(t, EXPR, "\n", "\n", extra_flags = { .Multiline })
+		check_expression(t, EXPR, "", "", extra_flags = { .Multiline })
+	}
+	{
+		EXPR :: `$`
+		check_expression(t, EXPR, "\n", "\n", extra_flags = { .Multiline })
+		check_expression(t, EXPR, "", "", extra_flags = { .Multiline })
+	}
+}
+
+@test
+test_optional_inside_optional :: proc(t: ^testing.T) {
+	EXPR :: `(?:a?)?`
+	check_expression(t, EXPR, "a", "a")
+	check_expression(t, EXPR, "", "")
+}
+
+@test
+test_printing :: proc(t: ^testing.T) {
+	rex, parse_err := regex.create(`^/a$`, {
+		.Global,
+		.Multiline,
+		.Case_Insensitive,
+		.Unicode,
+		.Ignore_Whitespace,
+		.No_Optimization,
+		.No_Capture,
+	})
+	if !testing.expect_value(t, parse_err, nil) {
+		return
+	}
+	defer regex.destroy(rex)
+
+	str := fmt.tprint(rex)
+	str_hash := fmt.tprintf("%#v", rex)
+	testing.expect_value(t, str, `/^\/a$/gmixun-`)
+	testing.expect_value(t, str_hash, `/^\/a$/gmixun-`)
+}
+
+
+
+@test
+test_error_bad_repetitions :: proc(t: ^testing.T) {
+	check_repetition_error :: proc(t: ^testing.T, pattern: string, loc := #caller_location) {
+		rex, err := regex.create(pattern)
+		regex.destroy(rex)
+		parse_err, _ := err.(regex.Parser_Error)
+		_, ok := parse_err.(parser.Invalid_Repetition)
+		if !ok {
+			log.errorf("expected error Invalid_Repetition, got %v", parse_err, location = loc)
+		}
+	}
+
+	check_repetition_error(t, "a{-1,2}")
+	check_repetition_error(t, "a{2,1}")
+	check_repetition_error(t, "a{bc}")
+	check_repetition_error(t, "a{,-3}")
+	check_repetition_error(t, "a{d,}")
+	check_repetition_error(t, "a{}")
+	check_repetition_error(t, "a{0,0}")
+	check_repetition_error(t, "a{,0}")
+	check_repetition_error(t, "a{,}")
+}
+
+@test
+test_error_invalid_unicode_in_pattern :: proc(t: ^testing.T) {
+	rex, err := regex.create("\xC0", { .Unicode })
+	regex.destroy(rex)
+	parse_err := err.(regex.Parser_Error)
+	_, ok := parse_err.(parser.Invalid_Unicode)
+	if !ok {
+		log.errorf("expected error Invalid_Unicode, got %v", parse_err)
+	}
+}
+
+@test
+test_error_invalid_unicode_in_string :: proc(t: ^testing.T) {
+	EXPR :: "^...$"
+	// NOTE: Matching on invalid Unicode is currently safe.
+	// If `utf8.decode_rune` ever changes, this test may fail.
+	check_expression(t, EXPR, "\xC0\xFF\xFE", "\xC0\xFF\xFE")
+}
+
+@test
+test_error_too_many_capture_groups :: proc(t: ^testing.T) {
+	// NOTE: There are 1 + 9 + 1 capture groups in this pattern.
+	// Remember the implicit capture group 0.
+	rex, err := regex.create("(1)(2)(3)(4)(5)(6)(7)(8)(9) (A)")
+	regex.destroy(rex)
+
+	parse_err, _ := err.(regex.Parser_Error)
+	_, ok := parse_err.(parser.Too_Many_Capture_Groups)
+	if !ok {
+		log.errorf("expected error Too_Many_Capture_Groups, got %v", parse_err)
+	}
+}
+
+@test
+test_error_unclosed_paren :: proc(t: ^testing.T) {
+	rex, err := regex.create("(Hellope")
+	regex.destroy(rex)
+
+	parse_err, _ := err.(regex.Parser_Error)
+	_, ok := parse_err.(parser.Expected_Token)
+	if !ok {
+		log.errorf("expected error Expected_Token, got %v", parse_err)
+	}
+}
+
+@test
+test_error_unclosed_class :: proc(t: ^testing.T) {
+	rex, err := regex.create("[helope")
+	regex.destroy(rex)
+
+	parse_err, _ := err.(regex.Parser_Error)
+	_, ok := parse_err.(parser.Unexpected_EOF)
+	if !ok {
+		log.errorf("expected error Unexpected_EOF, got %v", parse_err)
+	}
+}
+
+@test
+test_error_invalid_unicode_in_unclosed_class :: proc(t: ^testing.T) {
+	rex, err := regex.create("[\xC0", { .Unicode })
+	regex.destroy(rex)
+
+	parse_err, _ := err.(regex.Parser_Error)
+	_, ok := parse_err.(parser.Invalid_Unicode)
+	if !ok {
+		log.errorf("expected error Invalid_Unicode, got %v", parse_err)
+	}
+}
+
+@test
+test_program_too_big :: proc(t: ^testing.T) {
+	sb := strings.builder_make()
+	w := strings.to_writer(&sb)
+	defer strings.builder_destroy(&sb)
+
+	// Each byte will turn into two bytes for the whole opcode and operand,
+	// then the compiler will insert 5 more bytes for the Save instructions
+	// and the Match.
+	N :: common.MAX_PROGRAM_SIZE/2 - 2
+	for _ in 0..<N {
+		io.write_byte(w, 'a')
+	}
+
+	rex, err := regex.create(strings.to_string(sb))
+	regex.destroy(rex)
+
+	compile_err, _ := err.(regex.Compiler_Error)
+	testing.expect_value(t, compile_err, regex.Compiler_Error.Program_Too_Big)
+}
+
+@test
+test_too_many_classes :: proc(t: ^testing.T) {
+	sb := strings.builder_make()
+	w := strings.to_writer(&sb)
+	defer strings.builder_destroy(&sb)
+
+	N :: common.MAX_CLASSES
+	for i in 0..<rune(N) {
+		io.write_byte(w, '[')
+		io.write_rune(w, 'a' + i)
+		io.write_rune(w, 'b' + i)
+		io.write_byte(w, ']')
+	}
+
+	rex, err := regex.create(strings.to_string(sb))
+	regex.destroy(rex)
+
+	compile_err, _ := err.(regex.Compiler_Error)
+	testing.expect_value(t, compile_err, regex.Compiler_Error.Too_Many_Classes)
+}
+
+@test
+test_empty_captures :: proc(t: ^testing.T) {
+	rex, err := regex.create("(?:)()")
+	regex.destroy(rex)
+
+	parse_err, _ := err.(regex.Parser_Error)
+	token_err, ok := parse_err.(parser.Expected_Token)
+	if !ok {
+		log.errorf("expected error Expected_Token, got %v", parse_err)
+	} else {
+		testing.expect_value(t, token_err.kind, tokenizer.Token_Kind.Close_Paren)
+	}
+}
+
+@test
+test_lone_enders :: proc(t: ^testing.T) {
+	check_expression(t, `)`, ")", ")")
+	check_expression(t, `]`, "]", "]")
+}
+
+@test
+test_invalid_unary_tokens :: proc(t: ^testing.T) {
+	check_token_error :: proc(t: ^testing.T, pattern: string, loc := #caller_location) {
+		rex, err := regex.create(pattern)
+		regex.destroy(rex)
+		parse_err, _ := err.(regex.Parser_Error)
+		_, ok := parse_err.(parser.Invalid_Token)
+		if !ok {
+			log.errorf("expected error Invalid_Token, got %v", parse_err, location = loc)
+		}
+	}
+	check_token_error(t, `*`)
+	check_token_error(t, `*?`)
+	check_token_error(t, `+`)
+	check_token_error(t, `+?`)
+	check_token_error(t, `?`)
+	check_token_error(t, `??`)
+	check_token_error(t, `{}`)
+	check_token_error(t, `{1,}`)
+	check_token_error(t, `{1,2}`)
+	check_token_error(t, `{,2}`)
+
+	{
+		rex, err := regex.create(`\`)
+		regex.destroy(rex)
+		parse_err, _ := err.(regex.Parser_Error)
+		_, ok := parse_err.(parser.Unexpected_EOF)
+		if !ok {
+			log.errorf("expected error Unexpected_EOF, got %v", parse_err)
+		}
+	}
+}
+
+@test
+test_everything_at_once :: proc(t: ^testing.T) {
+	EXPR :: `# Comment up here.
+	^
+	a
+	.
+	(?:bc|ad)
+	e*                # A comment.
+	f+
+	g*?
+	h+?
+	i{0,1}
+	j{1,2}			#Tabbed-out comment.
+	k{,3}
+	l{4,}
+	m?
+	n??
+	[0-9]
+	(?:oo#)     # Another comment.
+	(p)
+	$
+# Comment down here.
+`
+
+	check_expression(t, EXPR, "a_bceeffgghhhijjklllllmn7oo#p", "a_bceeffgghhhijjklllllmn7oo#p", "p", extra_flags = { .Ignore_Whitespace })
+	check_expression(t, EXPR, "a_bcffhjkkklllln9oo#p", "a_bcffhjkkklllln9oo#p", "p", extra_flags = { .Ignore_Whitespace })
+}
+
+@test
+test_creation_from_user_string :: proc(t: ^testing.T) {
+	{
+		USER_EXPR :: `/^hellope$/gmixun-`
+		STR :: "hellope"
+		rex, err := regex.create_by_user(USER_EXPR)
+		defer regex.destroy(rex)
+		testing.expect_value(t, err, nil)
+		testing.expect_value(t, rex.flags, regex.Flags{ .Global, .Multiline, .Case_Insensitive, .Ignore_Whitespace, .Unicode, .No_Capture, .No_Optimization })
+
+		_, ok := regex.match(rex, STR)
+		testing.expectf(t, ok, "expected user-provided RegEx %v to match %q", rex, STR)
+	}
+	{
+		USER_EXPR :: `/\/var\/log/`
+		STR :: "/var/log"
+		rex, err := regex.create_by_user(USER_EXPR)
+		defer regex.destroy(rex)
+		testing.expect_value(t, err, nil)
+		testing.expect_value(t, rex.flags, regex.Flags{})
+
+		capture, ok := regex.match(rex, STR)
+		regex.destroy(capture)
+		testing.expectf(t, ok, "expected user-provided RegEx %v to match %q", rex, STR)
+	}
+	{
+		USER_EXPR :: `@@`
+		STR :: ""
+		rex, err := regex.create_by_user(USER_EXPR)
+		defer regex.destroy(rex)
+		testing.expect_value(t, err, nil)
+		testing.expect_value(t, rex.flags, regex.Flags{})
+
+		capture, ok := regex.match(rex, STR)
+		regex.destroy(capture)
+		testing.expectf(t, ok, "expected user-provided RegEx %v to match %q", rex, STR)
+	}
+	{
+		USER_EXPR :: `ほほ-`
+		STR :: ""
+		rex, err := regex.create_by_user(USER_EXPR)
+		defer regex.destroy(rex)
+		testing.expect_value(t, err, nil)
+		testing.expect_value(t, rex.flags, regex.Flags{ .No_Optimization })
+
+		capture, ok := regex.match(rex, STR)
+		regex.destroy(capture)
+		testing.expectf(t, ok, "expected user-provided RegEx %v to match %q", rex, STR)
+	}
+	{
+		USER_EXPR :: `ほ\ほほu`
+		STR :: "ほ"
+		rex, err := regex.create_by_user(USER_EXPR)
+		defer regex.destroy(rex)
+		testing.expect_value(t, err, nil)
+		testing.expect_value(t, rex.flags, regex.Flags{ .Unicode })
+
+		capture, ok := regex.match(rex, STR)
+		regex.destroy(capture)
+		testing.expectf(t, ok, "expected user-provided RegEx %v to match %q", rex, STR)
+	}
+	{
+		USER_EXPR :: `ふわふu`
+		STR :: "わ"
+		rex, err := regex.create_by_user(USER_EXPR)
+		defer regex.destroy(rex)
+		testing.expect_value(t, err, nil)
+		testing.expect_value(t, rex.flags, regex.Flags{ .Unicode })
+
+		capture, ok := regex.match(rex, STR)
+		regex.destroy(capture)
+		testing.expectf(t, ok, "expected user-provided RegEx %v to match %q", rex, STR)
+	}
+	{
+		USER_EXPR :: `なに`
+		_, err := regex.create_by_user(USER_EXPR)
+		testing.expect_value(t, err, regex.Creation_Error.Expected_Delimiter)
+	}
+	{
+		USER_EXPR :: `\o/`
+		_, err := regex.create_by_user(USER_EXPR)
+		testing.expect_value(t, err, regex.Creation_Error.Bad_Delimiter)
+	}
+	{
+		USER_EXPR :: `<=)<-<a`
+		_, err := regex.create_by_user(USER_EXPR)
+		testing.expect_value(t, err, regex.Creation_Error.Unknown_Flag)
+	}
+}
+
+
+
+// NOTE(Feoramund): The following are patterns I found out in the wild to test
+// coverage of how people might use RegEx.
+
+@test
+test_email_simple :: proc(t: ^testing.T) {
+	// Source: https://stackoverflow.com/a/50343015
+	EXPR :: `^[^@]+@[^@]+\.[^@]+$`
+	check_expression(t, EXPR, "bill@gingerbill.org", "bill@gingerbill.org")
+	check_expression(t, EXPR, "@not-an-email.com")
+}
+
+@test
+test_email_absurd :: proc(t: ^testing.T) {
+	// This is why you shouldn't use RegEx to parse rule-laden text.
+	// Source: https://emailregex.com/
+	EXPR :: `(?:[a-z0-9!#$%&'*+/=?^_` + "`" + `{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_` + "`" + `{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])`
+	check_expression(t, EXPR, "bill@gingerbill.org", "bill@gingerbill.org")
+	check_expression(t, EXPR, "@not-their own- typeemail.com") }
+
+@test
+test_uri_partition :: proc(t: ^testing.T) {
+	// Source: https://www.rfc-editor.org/rfc/rfc3986#appendix-B
+	EXPR :: `^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?`
+	check_expression(t, EXPR, "https://odin-lang.org/",
+		"https://odin-lang.org/",
+		"https:",
+		"https",
+		"//odin-lang.org",
+		"odin-lang.org",
+		"/")
+}
+
+@test
+test_ipv4 :: proc(t: ^testing.T) {
+	// Source: https://www.regular-expressions.info/ip.html
+	EXPR :: `\b(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\.
+	         (25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\.
+	         (25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\.
+	         (25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\b`
+	check_expression(t, EXPR, "127.0.0.1", "127.0.0.1", "127", "0", "0", "1", extra_flags = { .Ignore_Whitespace })
+	check_expression(t, EXPR, "9.9.9.9", "9.9.9.9", "9", "9", "9", "9", extra_flags = { .Ignore_Whitespace })
+}
+
+@test
+test_floating_point :: proc(t: ^testing.T) {
+	// Source: https://www.regular-expressions.info/floatingpoint.html
+	EXPR :: `[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?`
+	check_expression(t, EXPR, "-3.14", "-3.14")
+	check_expression(t, EXPR, "2.17", "2.17")
+	check_expression(t, EXPR, "1e9", "1e9", "e9")
+}
+
+@test
+test_uk_postal_code :: proc(t: ^testing.T) {
+	// Source: https://www.html5pattern.com/Postal_Codes
+	EXPR :: `[A-Za-z]{1,2}[0-9Rr][0-9A-Za-z]? [0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}`
+	check_expression(t, EXPR, "EC1A 1BB", "EC1A 1BB")
+}
+
+@test
+test_us_phone_number :: proc(t: ^testing.T) {
+	// Source: https://regexlib.com/REDetails.aspx?regexp_id=22
+	EXPR :: `^[2-9]\d{2}-\d{3}-\d{4}$`
+	check_expression(t, EXPR, "650-253-0001", "650-253-0001")
+}