tools: add vpm tests for installing modules with different URLs/identifiers (#19664)

cmd/tools/vpm/install_test.v

@@ -0,0 +1,43 @@
+import os
+import v.vmod
+
+// Running tests appends a tsession path to VTMP, which is automatically cleaned up after the test.
+// The following will result in e.g. `$VTMP/tsession_7fe8e93bd740_1612958707536/test-vmodules/`.
+const test_path = os.join_path(os.vtmp_dir(), 'test-vmodules')
+
+fn prep_test_path() {
+	os.setenv('VMODULES', test_path, true)
+}
+
+fn test_install_from_git_url() {
+	prep_test_path()
+	res := os.execute(@VEXE + ' install https://github.com/vlang/markdown')
+	mod := vmod.from_file(os.join_path(test_path, 'markdown', 'v.mod')) or {
+		assert false, err.str()
+		return
+	}
+	assert mod.name == 'markdown'
+	assert mod.dependencies == []string{}
+}
+
+fn test_install_from_vpm_ident() {
+	prep_test_path()
+	res := os.execute(@VEXE + ' install nedpals.args')
+	mod := vmod.from_file(os.join_path(test_path, 'nedpals', 'args', 'v.mod')) or {
+		assert false, err.str()
+		return
+	}
+	assert mod.name == 'nedpals.args'
+	assert mod.dependencies == []string{}
+}
+
+fn test_install_from_vpm_short_ident() {
+	prep_test_path()
+	res := os.execute(@VEXE + ' install pcre')
+	mod := vmod.from_file(os.join_path(test_path, 'pcre', 'v.mod')) or {
+		assert false, err.str()
+		return
+	}
+	assert mod.name == 'pcre'
+	assert mod.description == 'A simple regex library for V.'
+}