flutter_flutter/docs/contributing/testing/Flutter-Test-Fonts.md

Flutter tests run via the flutter test command have access to several readily available test fonts, including FlutterTest and Ahem.

In tests, if fontFamily isn't specified or the specified font families are not available, the default test font FlutterTest will be used. If you wish to use a custom font in tests, check out the FontLoader class, and this example.

The FlutterTest test font

Font Metrics (in design units)

	Ascent	Descent	Line Gap (Leading)	Units Per EM	Underline Position
FlutterTest	768 (0.75 em) above the baseline	256 (0.25 em) below the baseline	0	1024	146 under the baseline
Ahem	800 (0.8 em) above the baseline	200 (0.2 em) below the baseline	0	1000	142 under the baseline

The FlutterTest font's 1024 units-per-em is a power of 2, making it less likely to introduce precision loss in metrics calculations, when used as a divisor. Thanks to that, the FlutterTest font generally provides more precise and font-engine-agnostic font/glyph metrics than Ahem.

Example

You can expect this test to pass on all platforms:

final painter = TextPainter(
  text: const TextSpan(
    text: 'text',
    style: TextStyle(fontSize: 14.0, /* "fontFamily: 'FlutterTest'" is implied */),
  ),
  textDirection: TextDirection.ltr,
  textScaleFactor: 1.0,
);
final lineMetrics = textPainer.computeLineMetrics().first;

expect(lineMetrics.height, 14.0);
expect(lineMetrics.ascent, 10.5); // 0.75em * 14.0pt
expect(lineMetrics.descent, 3.5); // 0.25em * 14.0pt
// 'text' is 4 glyphs. Most glyphs are as wide as they are tall.
expect(lineMetrics.width, 14.0 * 4);

While with the Ahem font you would get slightly different metrics on different platforms, since they use different font engines to scale the font.

Glyphs

(images to be added)

The font covers most types of glyphs defined in the Ahem font.

Square	Ascent Flushed	Descent Flushed	.notdef
a box that fills the em square	the Square glyph but without the part above the baseline	the Square glyph but without the part below the baseline	a hollow box

The remaining glyphs (for example, Full Advance, 1/2 Advance) are defined with no outlines in the glyph, with different x-advances.

Glyph Mapping

Unmapped codepoints will be mapped to the .notdef glyph in the test environment.

\ Script Glyph	DFLT	grek	hani	latn
Square	codepoint(s): 0x21-0x26, 0x28-0x40, 0x5b-0x60, 0x7b-0x7e, 0xa1-0xa9, 0xab-0xb9, 0xbb-0xbf, 0xd7, 0xf7, 0x2c6-0x2c7, 0x2c9, 0x2d8-0x2dd, 0x2013-0x2014, 0x2018-0x201a, 0x201c-0x201e, 0x2020-0x2022, 0x2026, 0x2030, 0x2039-0x203a, 0x2044, 0x2122, 0x2202, 0x2206, 0x220f, 0x2211-0x2212, 0x2219-0x221a, 0x221e, 0x222b, 0x2248, 0x2260, 0x2264-0x2265, 0x22f2, 0x25ca, 0xf000-0xf002 character(s): ! " # $ % & ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? @ [ \ ] ^ _ ` { | } ~ ¡ ¢ £ ¤ ¥ ¦ § ¨ © « ¬ <SOFT HYPHEN> ® ¯ ° ± ² ³ ´ µ ¶ · ¸ ¹ » ¼ ½ ¾ ¿ × ÷ ˆ ˇ ˉ ˘ ˙ ˚ ˛ ˜ ˝ – — ‘ ’ ‚ “ ” „ † ‡ • … ‰ ‹ › ⁄ ™ ∂ ∆ ∏ ∑ − ∙ √ ∞ ∫ ≈ ≠ ≤ ≥ ⋲ ◊ <0xf000> <0xf001> <0xf002>	codepoint(s): 0x394, 0x3a5, 0x3a7, 0x3a9, 0x3bc, 0x3c0, 0x2126 character(s): Δ Υ Χ Ω μ π Ω	codepoint(s): 0x3007, 0x4e00, 0x4e03, 0x4e09, 0x4e2d, 0x4e5d, 0x4e8c, 0x4e94, 0x516b, 0x516d, 0x5341, 0x5426, 0x56d7, 0x56db, 0x571f, 0x6587, 0x6587, 0x662f, 0x6728, 0x672c, 0x6b63, 0x6c34, 0x6d4b, 0x706b, 0x786e, 0x8bd5, 0x91d1 character(s): 〇 一 七 三 中 九 二 五 八 六 十 否 囗 四 土 文 文 是 木 本 正 水 测 火 确 试 金	codepoint(s): 0x41-0x5a, 0x61-0x7a, 0xaa, 0xba, 0xc0-0xc8, 0xca-0xd6, 0xd8-0xf6, 0xf8-0xff, 0x131, 0x152-0x153, 0x178, 0x192 character(s): A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z ª º À Á Â Ã Ä Å Æ Ç È Ê Ë Ì Í Î Ï Ð Ñ Ò Ó Ô Õ Ö Ø Ù Ú Û Ü Ý Þ ß à á â ã ä å æ ç è é ê ë ì í î ï ð ñ ò ó ô õ ö ø ù ú û ü ý þ ÿ ı Œ œ Ÿ ƒ
Ascent Flushed				codepoint(s): 0x70 character(s): p
Descent Flushed				codepoint(s): 0xc9 character(s): É
Full Advance	codepoint(s): 0x20 character(s): <SPACE>
1/2 Advance	codepoint(s): 0x2002 character(s): <EN SPACE>
1/3 Advance	codepoint(s): 0x2004 character(s): <THREE-PER-EM SPACE>
1/4 Advance	codepoint(s): 0x2005 character(s): <FOUR-PER-EM SPACE>
1/6 Advance	codepoint(s): 0x2006 character(s): <SIX-PER-EM SPACE>
1/5 Advance	codepoint(s): 0x2009 character(s): <THIN SPACE>
1/10 Advance	codepoint(s): 0x200a character(s): <HAIR SPACE>
Zero Advance	codepoint(s): 0xfeff character(s): <ZERO WIDTH NO-BREAK SPACE>

Caveats

To disable FreeType auto-hinter, the family name defined within the font is not FlutterTest but MingLiU. This typically doesn't affect framework tests as the font is registered under the name FlutterTest.

Adding more Codepoints/Glyphs to the FlutterTest Font

The FlutterTest font is generated by this script.