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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 (currently with the exception of the web HTML renderer):

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.