{"id":576,"date":"2022-04-27T13:15:00","date_gmt":"2022-04-27T13:15:00","guid":{"rendered":"https:\/\/andrejacobs.org\/?p=576"},"modified":"2022-05-27T15:52:03","modified_gmt":"2022-05-27T15:52:03","slug":"learning-go-day-7","status":"publish","type":"post","link":"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-7\/","title":{"rendered":"Learning Go &#8211; Day 7"},"content":{"rendered":"\n<p class=\"has-small-font-size\">Featured image by&nbsp;<a href=\"https:\/\/github.com\/egonelbre\/gophers\" target=\"_blank\" rel=\"noreferrer noopener\">Egon Elbre<\/a><\/p>\n\n\n\n<div class=\"wp-block-jetpack-markdown\"><ul>\n<li>Counting words or lines from <code>stdin<\/code>.\n<ul>\n<li>os.Stdin implements the io.Reader inteface.<\/li>\n<li>bufio.Scanner can be used to iterate over words (ScanWords), lines (ScanLines), runes [aka Unicode characters] (ScanRunes) or bytes (ScanBytes).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<pre><code class=\"language-go\">import (\n\t&quot;bufio&quot;\n\t&quot;io&quot;\n\t&quot;os&quot;\n)\n\nfunc count(r io.Reader, countLines bool) int {\n\tscanner := bufio.NewScanner(r)\n\n\tif !countLines {\n\t\tscanner.Split(bufio.ScanWords)\n\t}\n\n\twc := 0\n\n\tfor scanner.Scan() {\n\t\twc++\n\t}\n\n\treturn wc\n}\n\n\/\/ Count words\ncount(os.Stdin, false)\n\/\/ Count lines (\\n) [except the trailing one]\ncount(os.Stdin, true)\n<\/code><\/pre>\n<ul>\n<li>Playing well with others the Unix way. Meaning write error messages to <code>stderr<\/code> (and not <code>stdout<\/code>) and return non zero exit codes.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">if err := someOperation(); err != nil {\n\t\tfmt.Fprintln(os.Stderr, err)\n\t\tos.Exit(42)\n}\n<\/code><\/pre>\n<ul>\n<li>The arguments passed to a go application can be accessed with <code>os.Args<\/code> (which is declared as <code>var Args []string<\/code> in the os package). Remember item 0 is the path of the application and thus you can use <code>Args[1:]<\/code> to return the slice of only the passed arguments.<\/li>\n<li>Visual Studio Code can easilly navigate to the source code for any standard library by just Cmd+Click on the name.<\/li>\n<li>You can determine the platform the app is running on by querying things from the <code>runtime<\/code> package. For example <code>runtime.GOOS == &quot;windows&quot;<\/code>.<\/li>\n<\/ul>\n<h3>Unit-testing<\/h3>\n<p>Generally all .go files in the same directory has to belong to the same Go package except for unit-tests that are allowed to belong to a different package. This helps ensure that your package only exports the types and functions\/methods as you intended and thus the unit-test can only import what you exported.<\/p>\n<p>Convention is to name unit-test files with the <code>_test.go<\/code> suffix and also for the package name.<\/p>\n<p>Example: main.go will be unit-tested with main_test.go and that has a <code>package main_test<\/code> as the first line.<\/p>\n<ul>\n<li>Tests can be run with more verbosity.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">$ go test -v\n=== RUN   TestOne\n--- PASS: TestOne (0.00s)\n=== RUN   TestSomething\n--- PASS: TestSomething (0.00s)\n=== RUN   TestTwo\n--- PASS: TestTwo (0.00s)\nPASS\nok      todo    0.097s\n\n$ go test -v\n=== RUN   TestOne\n--- FAIL: TestOne (0.00s)\n...\n<\/code><\/pre>\n<ul>\n<li>Visual Studio Code makes unit-testing really nice and even does code coverage with highlighting the code that was covered.<\/li>\n<\/ul>\n<p><img decoding=\"async\" src=\"https:\/\/andrejacobs.org\/wp-content\/uploads\/2022\/05\/Untitled.png\" alt=\"\"><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/andrejacobs.org\/wp-content\/uploads\/2022\/05\/Untitled-1.png\" alt=\"\"><\/p>\n<ul>\n<li>Tests can be run with code coverage and a specified timeout. This is what VS Code uses.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">$ go test -timeout 30s -coverprofile=\/path\/to\/codecoverage packagename\n<\/code><\/pre>\n<ul>\n<li>To run an individual test.\nNote that you actually specify a regex of which tests to run. In this case a function matching \u201cTestAdd\u201d in the package \u201ctodo\u201d.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">$ go test -timeout 30s -run ^TestAdd$ todo\n<\/code><\/pre>\n<ul>\n<li>Example of a unit-test function. Note that unit-tests are declared with a prefix \u201cTest\u201d and the argument is <code>(t *testing.T)<\/code>.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">package todo_test\n\nimport (\n\t&quot;testing&quot;\n\t&quot;todo&quot;\n)\n\nfunc TestAdd(t *testing.T) {\n\t\/\/ Do something you want to test\n\t...\n\n\tif result != expected {\n\t\tt.Errorf(&quot;Expected %q, got %q\\n&quot;, expected, result)\n\t}\n}\n<\/code><\/pre>\n<ul>\n<li>To see an awesome way of doing an integration test of your CLI app, by which the unit-test compiles the app, runs and test the app. See the code for \u201cinteracting\/todo\/cmd\/main_test.go\u201d from this <a href=\"https:\/\/pragprog.com\/titles\/rggo\/powerful-command-line-applications-in-go\/\">book<\/a>\u2019s source code.<\/li>\n<li>You can place resource files to be used by your tests in a special directory called <code>testdata<\/code>. The Go tooling will ignore these files.<\/li>\n<\/ul>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Featured image by&nbsp;Egon Elbre [&#8230;]<\/p>\n<p><a class=\"understrap-read-more-link\" href=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-7\/\">Read more &rarr;<\/a><\/p>\n","protected":false},"author":2,"featured_media":581,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_mi_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[52],"tags":[53],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v19.13 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Learning Go - Day 7 - Andr\u00e9 Jacobs<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-7\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Learning Go - Day 7 - Andr\u00e9 Jacobs\" \/>\n<meta property=\"og:description\" content=\"Featured image by&nbsp;Egon Elbre [...]Read more &rarr;\" \/>\n<meta property=\"og:url\" content=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-7\/\" \/>\n<meta property=\"og:site_name\" content=\"Andr\u00e9 Jacobs\" \/>\n<meta property=\"article:published_time\" content=\"2022-04-27T13:15:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2022-05-27T15:52:03+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/andrejacobs.org\/wp-content\/uploads\/2022\/05\/saxophone.png\" \/>\n\t<meta property=\"og:image:width\" content=\"315\" \/>\n\t<meta property=\"og:image:height\" content=\"397\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"Andr\u00e9 Jacobs\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@andrejacobs81\" \/>\n<meta name=\"twitter:site\" content=\"@andrejacobs81\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Andr\u00e9 Jacobs\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-7\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-7\/\"},\"author\":{\"name\":\"Andr\u00e9 Jacobs\",\"@id\":\"https:\/\/andrejacobs.org\/#\/schema\/person\/3d38360883015e883c80c2fb875c5a68\"},\"headline\":\"Learning Go &#8211; 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